Original patch by James Edwards.
line = f.readline()
if not line:
break
- ... # do something with line
+ ... # do something with line
The reason for not allowing assignment in Python expressions is a common,
hard-to-find bug in those other languages, caused by this construct:
line = f.readline()
while line:
- ... # do something with line...
+ ... # do something with line...
line = f.readline()
The problem with this is that if you change your mind about exactly how you get
Python file objects support the iterator protocol, so you can now write simply::
for line in f:
- ... # do something with line...
+ ... # do something with line...
class ListWrapper:
def __init__(self, the_list):
self.the_list = the_list
+
def __eq__(self, other):
return self.the_list == other.the_list
+
def __hash__(self):
l = self.the_list
result = 98767 - len(l)*555
order::
for key in sorted(mydict):
- ... # do whatever with mydict[key]...
+ ... # do whatever with mydict[key]...
How do you specify and enforce an interface spec in Python?
class label: pass # declare a label
try:
- ...
- if condition: raise label() # goto label
- ...
+ ...
+ if condition: raise label() # goto label
+ ...
except label: # where to goto
- pass
+ pass
...
This doesn't allow you to jump into the middle of a loop, but that's usually
import httplib, sys, time
- ### build the query string
+ # build the query string
qs = "First=Josephine&MI=Q&Last=Public"
- ### connect and send the server a path
+ # connect and send the server a path
httpobj = httplib.HTTP('www.some-server.out-there', 80)
httpobj.putrequest('POST', '/cgi-bin/some-cgi-script')
- ### now generate the rest of the HTTP headers...
+ # now generate the rest of the HTTP headers...
httpobj.putheader('Accept', '*/*')
httpobj.putheader('Connection', 'Keep-Alive')
httpobj.putheader('Content-type', 'application/x-www-form-urlencoded')
httpobj.putheader('Content-length', '%d' % len(qs))
httpobj.endheaders()
httpobj.send(qs)
- ### find out what the server said in response...
+ # find out what the server said in response...
reply, msg, hdrs = httpobj.getreply()
if reply != 200:
sys.stdout.write(httpobj.getfile().read())
``/usr/sbin/sendmail``. The sendmail manual page will help you out. Here's
some sample code::
- SENDMAIL = "/usr/sbin/sendmail" # sendmail location
import os
+
+ SENDMAIL = "/usr/sbin/sendmail" # sendmail location
p = os.popen("%s -t -i" % SENDMAIL, "w")
p.write("To: receiver@example.com\n")
p.write("Subject: test\n")
>>> squares = []
>>> for x in range(5):
- ... squares.append(lambda: x**2)
+ ... squares.append(lambda: x**2)
This gives you a list that contains 5 lambdas that calculate ``x**2``. You
might expect that, when called, they would return, respectively, ``0``, ``1``,
>>> squares = []
>>> for x in range(5):
- ... squares.append(lambda n=x: n**2)
+ ... squares.append(lambda n=x: n**2)
Here, ``n=x`` creates a new variable ``n`` local to the lambda and computed
when the lambda is defined so that it has the same value that ``x`` had at
args['a'] = 'new-value' # args is a mutable dictionary
args['b'] = args['b'] + 1 # change it in-place
- args = {'a':' old-value', 'b': 99}
+ args = {'a': 'old-value', 'b': 99}
func3(args)
print args['a'], args['b']
``def`` and ``class`` statements, but in that case the value is a
callable. Consider the following code::
- class A:
- pass
-
- B = A
-
- a = B()
- b = a
- print b
+ >>> class A:
+ ... pass
+ ...
+ >>> B = A
+ >>> a = B()
+ >>> b = a
+ >>> print b
<__main__.A instance at 0x16D07CC>
- print a
+ >>> print a
<__main__.A instance at 0x16D07CC>
Arguably the class has a name: even though it is bound to two names and invoked
Use the :func:`reversed` built-in function, which is new in Python 2.4::
for x in reversed(sequence):
- ... # do something with x...
+ ... # do something with x ...
This won't touch your original sequence, but build a new copy with reversed
order to iterate over.
With Python 2.3, you can use an extended slice syntax::
for x in sequence[::-1]:
- ... # do something with x...
+ ... # do something with x ...
How do you remove duplicates from a list?
definition::
class C:
- def meth (self, arg):
+ def meth(self, arg):
return arg * 2 + self.attribute
def search(obj):
if isinstance(obj, Mailbox):
- # ... code to search a mailbox
+ ... # code to search a mailbox
elif isinstance(obj, Document):
- # ... code to search a document
+ ... # code to search a document
elif ...
A better approach is to define a ``search()`` method on all the classes and just
class Mailbox:
def search(self):
- # ... code to search a mailbox
+ ... # code to search a mailbox
class Document:
def search(self):
- # ... code to search a document
+ ... # code to search a document
obj.search()
If you're using new-style classes, use the built-in :func:`super` function::
class Derived(Base):
- def meth (self):
+ def meth(self):
super(Derived, self).meth()
If you're using classic classes: For a class definition such as ``class
"Emulate type_getattro() in Objects/typeobject.c"
v = object.__getattribute__(self, key)
if hasattr(v, '__get__'):
- return v.__get__(None, self)
+ return v.__get__(None, self)
return v
The important points to remember are:
self.val = val
>>> class MyClass(object):
- x = RevealAccess(10, 'var "x"')
- y = 5
-
+ ... x = RevealAccess(10, 'var "x"')
+ ... y = 5
+ ...
>>> m = MyClass()
>>> m.x
Retrieving var "x"
Running the interpreter shows how the function descriptor works in practice::
>>> class D(object):
- def f(self, x):
- return x
-
+ ... def f(self, x):
+ ... return x
+ ...
>>> d = D()
- >>> D.__dict__['f'] # Stored internally as a function
+ >>> D.__dict__['f'] # Stored internally as a function
<function f at 0x00C45070>
- >>> D.f # Get from a class becomes an unbound method
+ >>> D.f # Get from a class becomes an unbound method
<unbound method D.f>
- >>> d.f # Get from an instance becomes a bound method
+ >>> d.f # Get from an instance becomes a bound method
<bound method D.f of <__main__.D object at 0x00B18C90>>
The output suggests that bound and unbound methods are two different types.
calls are unexciting::
>>> class E(object):
- def f(x):
- print x
- f = staticmethod(f)
-
+ ... def f(x):
+ ... print x
+ ... f = staticmethod(f)
+ ...
>>> print E.f(3)
3
>>> print E().f(3)
:func:`staticmethod` would look like this::
class StaticMethod(object):
- "Emulate PyStaticMethod_Type() in Objects/funcobject.c"
+ "Emulate PyStaticMethod_Type() in Objects/funcobject.c"
- def __init__(self, f):
- self.f = f
+ def __init__(self, f):
+ self.f = f
- def __get__(self, obj, objtype=None):
- return self.f
+ def __get__(self, obj, objtype=None):
+ return self.f
Unlike static methods, class methods prepend the class reference to the
argument list before calling the function. This format is the same
for whether the caller is an object or a class::
>>> class E(object):
- def f(klass, x):
- return klass.__name__, x
- f = classmethod(f)
-
+ ... def f(klass, x):
+ ... return klass.__name__, x
+ ... f = classmethod(f)
+ ...
>>> print E.f(3)
('E', 3)
>>> print E().f(3)
:func:`classmethod` would look like this::
class ClassMethod(object):
- "Emulate PyClassMethod_Type() in Objects/funcobject.c"
+ "Emulate PyClassMethod_Type() in Objects/funcobject.c"
- def __init__(self, f):
- self.f = f
+ def __init__(self, f):
+ self.f = f
- def __get__(self, obj, klass=None):
- if klass is None:
- klass = type(obj)
- def newfunc(*args):
- return self.f(klass, *args)
- return newfunc
+ def __get__(self, obj, klass=None):
+ if klass is None:
+ klass = type(obj)
+ def newfunc(*args):
+ return self.f(klass, *args)
+ return newfunc
continue # Skip this element
for expr2 in sequence2:
if not (condition2):
- continue # Skip this element
+ continue # Skip this element
...
for exprN in sequenceN:
- if not (conditionN):
- continue # Skip this element
+ if not (conditionN):
+ continue # Skip this element
- # Output the value of
- # the expression.
+ # Output the value of
+ # the expression.
This means that when there are multiple ``for...in`` clauses but no ``if``
clauses, the length of the resulting output will be equal to the product of the
def __init__(self):
self.logger = logging.getLogger('spam_application.auxiliary.Auxiliary')
self.logger.info('creating an instance of Auxiliary')
+
def do_something(self):
self.logger.info('doing something')
a = 1 + 1
return True
if __name__ == '__main__':
- levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
- logging.basicConfig(level=logging.DEBUG,
- format='%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s')
- a1 = logging.getLogger('a.b.c')
- a2 = logging.getLogger('d.e.f')
-
- f = ContextFilter()
- a1.addFilter(f)
- a2.addFilter(f)
- a1.debug('A debug message')
- a1.info('An info message with %s', 'some parameters')
- for x in range(10):
- lvl = choice(levels)
- lvlname = logging.getLevelName(lvl)
- a2.log(lvl, 'A message at %s level with %d %s', lvlname, 2, 'parameters')
+ levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
+ logging.basicConfig(level=logging.DEBUG,
+ format='%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s')
+ a1 = logging.getLogger('a.b.c')
+ a2 = logging.getLogger('d.e.f')
+
+ f = ContextFilter()
+ a1.addFilter(f)
+ a2.addFilter(f)
+ a1.debug('A debug message')
+ a1.info('An info message with %s', 'some parameters')
+ for x in range(10):
+ lvl = choice(levels)
+ lvlname = logging.getLevelName(lvl)
+ a2.log(lvl, 'A message at %s level with %d %s', lvlname, 2, 'parameters')
which, when run, produces something like::
A very simple example is::
import logging
- logging.warning('Watch out!') # will print a message to the console
- logging.info('I told you so') # will not print anything
+ logging.warning('Watch out!') # will print a message to the console
+ logging.info('I told you so') # will not print anything
If you type these lines into a script and run it, you'll see::
Here's a simple example of using the :meth:`sub` method. It replaces colour
names with the word ``colour``::
- >>> p = re.compile( '(blue|white|red)')
- >>> p.sub( 'colour', 'blue socks and red shoes')
+ >>> p = re.compile('(blue|white|red)')
+ >>> p.sub('colour', 'blue socks and red shoes')
'colour socks and colour shoes'
- >>> p.sub( 'colour', 'blue socks and red shoes', count=1)
+ >>> p.sub('colour', 'blue socks and red shoes', count=1)
'colour socks and red shoes'
The :meth:`subn` method does the same work, but returns a 2-tuple containing the
new string value and the number of replacements that were performed::
- >>> p = re.compile( '(blue|white|red)')
- >>> p.subn( 'colour', 'blue socks and red shoes')
+ >>> p = re.compile('(blue|white|red)')
+ >>> p.subn('colour', 'blue socks and red shoes')
('colour socks and colour shoes', 2)
- >>> p.subn( 'colour', 'no colours at all')
+ >>> p.subn('colour', 'no colours at all')
('no colours at all', 0)
Empty matches are replaced only when they're not adjacent to a previous match.
url = 'http://www.someserver.com/cgi-bin/register.cgi'
user_agent = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64)'
- values = {'name' : 'Michael Foord',
- 'location' : 'Northampton',
- 'language' : 'Python' }
- headers = { 'User-Agent' : user_agent }
+ values = {'name': 'Michael Foord',
+ 'location': 'Northampton',
+ 'language': 'Python' }
+ headers = {'User-Agent': user_agent}
data = urllib.urlencode(values)
req = urllib2.Request(url, data, headers)
yield '<h1>FastCGI Environment</h1>'
yield '<table>'
for k, v in sorted(environ.items()):
- yield '<tr><th>%s</th><td>%s</td></tr>' % (escape(k), escape(v))
+ yield '<tr><th>%s</th><td>%s</td></tr>' % (escape(k), escape(v))
yield '</table>'
WSGIServer(app).run()
parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument('integers', metavar='N', type=int, nargs='+',
- help='an integer for the accumulator')
+ help='an integer for the accumulator')
parser.add_argument('--sum', dest='accumulate', action='store_const',
- const=sum, default=max,
- help='sum the integers (default: find the max)')
+ const=sum, default=max,
+ help='sum the integers (default: find the max)')
args = parser.parse_args()
print args.accumulate(args.integers)
arguments they contain. For example::
>>> with open('args.txt', 'w') as fp:
- ... fp.write('-f\nbar')
+ ... fp.write('-f\nbar')
>>> parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
>>> parser.add_argument('-f')
>>> parser.parse_args(['-f', 'foo', '@args.txt'])
>>> parser = argparse.ArgumentParser(prog='frobble')
>>> parser.add_argument('--foo', action='store_true',
- ... help='foo the bars before frobbling')
+ ... help='foo the bars before frobbling')
>>> parser.add_argument('bar', nargs='+',
- ... help='one of the bars to be frobbled')
+ ... help='one of the bars to be frobbled')
>>> parser.parse_args(['-h'])
usage: frobble [-h] [--foo] bar [bar ...]
>>> parser = argparse.ArgumentParser(prog='frobble')
>>> parser.add_argument('bar', nargs='?', type=int, default=42,
- ... help='the bar to %(prog)s (default: %(default)s)')
+ ... help='the bar to %(prog)s (default: %(default)s)')
>>> parser.print_help()
usage: frobble [-h] [bar]
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument(
... 'integers', metavar='int', type=int, choices=xrange(10),
- ... nargs='+', help='an integer in the range 0..9')
+ ... nargs='+', help='an integer in the range 0..9')
>>> parser.add_argument(
... '--sum', dest='accumulate', action='store_const', const=sum,
- ... default=max, help='sum the integers (default: find the max)')
+ ... default=max, help='sum the integers (default: find the max)')
>>> parser.parse_args(['1', '2', '3', '4'])
Namespace(accumulate=<built-in function max>, integers=[1, 2, 3, 4])
>>> parser.parse_args(['1', '2', '3', '4', '--sum'])
self.set_terminator(None)
self.handle_request()
elif not self.handling:
- self.set_terminator(None) # browsers sometimes over-send
+ self.set_terminator(None) # browsers sometimes over-send
self.cgi_data = parse(self.headers, "".join(self.ibuffer))
self.handling = True
self.ibuffer = []
# out_test)
prefill = '\0'*(pos+ipos)*2
postfill = '\0'*(len(inputdata)-len(prefill)-len(outputdata))
- outputdata = prefill + audioop.mul(outputdata,2,-factor) + postfill
+ outputdata = prefill + audioop.mul(outputdata, 2, -factor) + postfill
return audioop.add(inputdata, outputdata, 2)
in conjuction with sorting to make a sorted dictionary::
>>> # regular unsorted dictionary
- >>> d = {'banana': 3, 'apple':4, 'pear': 1, 'orange': 2}
+ >>> d = {'banana': 3, 'apple': 4, 'pear': 1, 'orange': 2}
>>> # dictionary sorted by key
>>> OrderedDict(sorted(d.items(), key=lambda t: t[0]))
for value in iterable:
if value not in lst:
lst.append(value)
+
def __iter__(self):
return iter(self.elements)
+
def __contains__(self, value):
return value in self.elements
+
def __len__(self):
return len(self.elements)
config.read('example.cfg')
# Set the third, optional argument of get to 1 if you wish to use raw mode.
- print config.get('Section1', 'foo', 0) # -> "Python is fun!"
- print config.get('Section1', 'foo', 1) # -> "%(bar)s is %(baz)s!"
+ print config.get('Section1', 'foo', 0) # -> "Python is fun!"
+ print config.get('Section1', 'foo', 1) # -> "%(bar)s is %(baz)s!"
# The optional fourth argument is a dict with members that will take
# precedence in interpolation.
config = ConfigParser.SafeConfigParser({'bar': 'Life', 'baz': 'hard'})
config.read('example.cfg')
- print config.get('Section1', 'foo') # -> "Python is fun!"
+ print config.get('Section1', 'foo') # -> "Python is fun!"
config.remove_option('Section1', 'bar')
config.remove_option('Section1', 'baz')
- print config.get('Section1', 'foo') # -> "Life is hard!"
+ print config.get('Section1', 'foo') # -> "Life is hard!"
The function ``opt_move`` below can be used to move options between sections::
convention::
>>> from ctypes import *
- >>> print windll.kernel32 # doctest: +WINDOWS
+ >>> print windll.kernel32 # doctest: +WINDOWS
<WinDLL 'kernel32', handle ... at ...>
- >>> print cdll.msvcrt # doctest: +WINDOWS
+ >>> print cdll.msvcrt # doctest: +WINDOWS
<CDLL 'msvcrt', handle ... at ...>
- >>> libc = cdll.msvcrt # doctest: +WINDOWS
+ >>> libc = cdll.msvcrt # doctest: +WINDOWS
>>>
Windows appends the usual ``.dll`` file suffix automatically.
:meth:`LoadLibrary` method of the dll loaders should be used, or you should load
the library by creating an instance of CDLL by calling the constructor::
- >>> cdll.LoadLibrary("libc.so.6") # doctest: +LINUX
+ >>> cdll.LoadLibrary("libc.so.6") # doctest: +LINUX
<CDLL 'libc.so.6', handle ... at ...>
- >>> libc = CDLL("libc.so.6") # doctest: +LINUX
- >>> libc # doctest: +LINUX
+ >>> libc = CDLL("libc.so.6") # doctest: +LINUX
+ >>> libc # doctest: +LINUX
<CDLL 'libc.so.6', handle ... at ...>
>>>
>>> from ctypes import *
>>> libc.printf
<_FuncPtr object at 0x...>
- >>> print windll.kernel32.GetModuleHandleA # doctest: +WINDOWS
+ >>> print windll.kernel32.GetModuleHandleA # doctest: +WINDOWS
<_FuncPtr object at 0x...>
- >>> print windll.kernel32.MyOwnFunction # doctest: +WINDOWS
+ >>> print windll.kernel32.MyOwnFunction # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "ctypes.py", line 239, in __getattr__
identifiers, like ``"??2@YAPAXI@Z"``. In this case you have to use
:func:`getattr` to retrieve the function::
- >>> getattr(cdll.msvcrt, "??2@YAPAXI@Z") # doctest: +WINDOWS
+ >>> getattr(cdll.msvcrt, "??2@YAPAXI@Z") # doctest: +WINDOWS
<_FuncPtr object at 0x...>
>>>
On Windows, some dlls export functions not by name but by ordinal. These
functions can be accessed by indexing the dll object with the ordinal number::
- >>> cdll.kernel32[1] # doctest: +WINDOWS
+ >>> cdll.kernel32[1] # doctest: +WINDOWS
<_FuncPtr object at 0x...>
- >>> cdll.kernel32[0] # doctest: +WINDOWS
+ >>> cdll.kernel32[0] # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "ctypes.py", line 310, in __getitem__
This example calls both functions with a NULL pointer (``None`` should be used
as the NULL pointer)::
- >>> print libc.time(None) # doctest: +SKIP
+ >>> print libc.time(None) # doctest: +SKIP
1150640792
- >>> print hex(windll.kernel32.GetModuleHandleA(None)) # doctest: +WINDOWS
+ >>> print hex(windll.kernel32.GetModuleHandleA(None)) # doctest: +WINDOWS
0x1d000000
>>>
Windows. It does this by examining the stack after the function returns, so
although an error is raised the function *has* been called::
- >>> windll.kernel32.GetModuleHandleA() # doctest: +WINDOWS
+ >>> windll.kernel32.GetModuleHandleA() # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: Procedure probably called with not enough arguments (4 bytes missing)
- >>> windll.kernel32.GetModuleHandleA(0, 0) # doctest: +WINDOWS
+ >>> windll.kernel32.GetModuleHandleA(0, 0) # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: Procedure probably called with too many arguments (4 bytes in excess)
The same exception is raised when you call an ``stdcall`` function with the
``cdecl`` calling convention, or vice versa::
- >>> cdll.kernel32.GetModuleHandleA(None) # doctest: +WINDOWS
+ >>> cdll.kernel32.GetModuleHandleA(None) # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: Procedure probably called with not enough arguments (4 bytes missing)
>>>
- >>> windll.msvcrt.printf("spam") # doctest: +WINDOWS
+ >>> windll.msvcrt.printf("spam") # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: Procedure probably called with too many arguments (4 bytes in excess)
crashes from general protection faults when functions are called with invalid
argument values::
- >>> windll.kernel32.GetModuleHandleA(32) # doctest: +WINDOWS
+ >>> windll.kernel32.GetModuleHandleA(32) # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
WindowsError: exception: access violation reading 0x00000020
a string pointer and a char, and returns a pointer to a string::
>>> strchr = libc.strchr
- >>> strchr("abcdef", ord("d")) # doctest: +SKIP
+ >>> strchr("abcdef", ord("d")) # doctest: +SKIP
8059983
- >>> strchr.restype = c_char_p # c_char_p is a pointer to a string
+ >>> strchr.restype = c_char_p # c_char_p is a pointer to a string
>>> strchr("abcdef", ord("d"))
'def'
>>> print strchr("abcdef", ord("x"))
result of this call will be used as the result of your function call. This is
useful to check for error return values and automatically raise an exception::
- >>> GetModuleHandle = windll.kernel32.GetModuleHandleA # doctest: +WINDOWS
+ >>> GetModuleHandle = windll.kernel32.GetModuleHandleA # doctest: +WINDOWS
>>> def ValidHandle(value):
... if value == 0:
... raise WinError()
... return value
...
>>>
- >>> GetModuleHandle.restype = ValidHandle # doctest: +WINDOWS
- >>> GetModuleHandle(None) # doctest: +WINDOWS
+ >>> GetModuleHandle.restype = ValidHandle # doctest: +WINDOWS
+ >>> GetModuleHandle(None) # doctest: +WINDOWS
486539264
- >>> GetModuleHandle("something silly") # doctest: +WINDOWS
+ >>> GetModuleHandle("something silly") # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in ValidHandle
>>> from ctypes import *
>>> class POINT(Structure):
- ... _fields_ = ("x", c_int), ("y", c_int)
+ ... _fields_ = ("x", c_int), ("y", c_int)
...
>>> class MyStruct(Structure):
- ... _fields_ = [("a", c_int),
- ... ("b", c_float),
- ... ("point_array", POINT * 4)]
+ ... _fields_ = [("a", c_int),
+ ... ("b", c_float),
+ ... ("point_array", POINT * 4)]
>>>
>>> print len(MyStruct().point_array)
4
It is funny to see that on linux the sort function seems to work much more
efficiently, it is doing less comparisons::
- >>> qsort(ia, len(ia), sizeof(c_int), cmp_func) # doctest: +LINUX
+ >>> qsort(ia, len(ia), sizeof(c_int), cmp_func) # doctest: +LINUX
py_cmp_func 5 1
py_cmp_func 33 99
py_cmp_func 7 33
hit the NULL entry::
>>> for item in table:
- ... print item.name, item.size
- ... if item.name is None:
- ... break
+ ... print item.name, item.size
+ ... if item.name is None:
+ ... break
...
__hello__ 104
__phello__ -104
opts, args = getopt.getopt(sys.argv[1:], "ho:v", ["help", "output="])
except getopt.GetoptError as err:
# print help information and exit:
- print str(err) # will print something like "option -a not recognized"
+ print str(err) # will print something like "option -a not recognized"
usage()
sys.exit(2)
output = None
class MyHTMLParser(HTMLParser):
def handle_starttag(self, tag, attrs):
print "Encountered a start tag:", tag
+
def handle_endtag(self, tag):
print "Encountered an end tag :", tag
+
def handle_data(self, data):
print "Encountered some data :", data
print "Start tag:", tag
for attr in attrs:
print " attr:", attr
+
def handle_endtag(self, tag):
print "End tag :", tag
+
def handle_data(self, data):
print "Data :", data
+
def handle_comment(self, data):
print "Comment :", data
+
def handle_entityref(self, name):
c = unichr(name2codepoint[name])
print "Named ent:", c
+
def handle_charref(self, name):
if name.startswith('x'):
c = unichr(int(name[1:], 16))
else:
c = unichr(int(name))
print "Num ent :", c
+
def handle_decl(self, data):
print "Decl :", data
attr: ('type', 'text/css')
Data : #python { color: green }
End tag : style
- >>>
+
>>> parser.feed('<script type="text/javascript">'
... 'alert("<strong>hello!</strong>");</script>')
Start tag: script
Example::
>>> import locale
- >>> loc = locale.getlocale() # get current locale
+ >>> loc = locale.getlocale() # get current locale
# use German locale; name might vary with platform
>>> locale.setlocale(locale.LC_ALL, 'de_DE')
- >>> locale.strcoll('f\xe4n', 'foo') # compare a string containing an umlaut
- >>> locale.setlocale(locale.LC_ALL, '') # use user's preferred locale
- >>> locale.setlocale(locale.LC_ALL, 'C') # use default (C) locale
- >>> locale.setlocale(locale.LC_ALL, loc) # restore saved locale
+ >>> locale.strcoll('f\xe4n', 'foo') # compare a string containing an umlaut
+ >>> locale.setlocale(locale.LC_ALL, '') # use user's preferred locale
+ >>> locale.setlocale(locale.LC_ALL, 'C') # use default (C) locale
+ >>> locale.setlocale(locale.LC_ALL, loc) # restore saved locale
Background, details, hints, tips and caveats
An example usage::
>>> import mailcap
- >>> d=mailcap.getcaps()
+ >>> d = mailcap.getcaps()
>>> mailcap.findmatch(d, 'video/mpeg', filename='tmp1223')
('xmpeg tmp1223', {'view': 'xmpeg %s'})
pid = os.fork()
- if pid == 0: # In a child process
+ if pid == 0: # In a child process
mm.seek(0)
print mm.readline()
... do something using "lock" ...
if __name__ == '__main__':
- lock = Lock()
- for i in range(10):
+ lock = Lock()
+ for i in range(10):
Process(target=f).start()
should be rewritten as ::
... do something using "l" ...
if __name__ == '__main__':
- lock = Lock()
- for i in range(10):
+ lock = Lock()
+ for i in range(10):
Process(target=f, args=(lock,)).start()
Beware of replacing :data:`sys.stdin` with a "file like object"
Here's an example of using :mod:`optparse` in a simple script::
from optparse import OptionParser
- [...]
+ ...
parser = OptionParser()
parser.add_option("-f", "--file", dest="filename",
help="write report to FILE", metavar="FILE")
program, create an OptionParser instance::
from optparse import OptionParser
- [...]
+ ...
parser = OptionParser()
Then you can start defining options. The basic syntax is::
condition::
(options, args) = parser.parse_args()
- [...]
+ ...
if options.a and options.b:
parser.error("options -a and -b are mutually exclusive")
Here's what :mod:`optparse`\ -based scripts usually look like::
from optparse import OptionParser
- [...]
+ ...
def main():
usage = "usage: %prog [options] arg"
parser = OptionParser(usage)
action="store_true", dest="verbose")
parser.add_option("-q", "--quiet",
action="store_false", dest="verbose")
- [...]
+ ...
(options, args) = parser.parse_args()
if len(args) != 1:
parser.error("incorrect number of arguments")
if options.verbose:
print "reading %s..." % options.filename
- [...]
+ ...
if __name__ == "__main__":
main()
strings::
parser.add_option("-n", "--dry-run", ...)
- [...]
+ ...
parser.add_option("-n", "--noisy", ...)
(This is particularly true if you've defined your own OptionParser subclass with
Options:
--dry-run do no harm
- [...]
+ ...
-n, --noisy be noisy
It's possible to whittle away the option strings for a previously-added option
accessible, so :mod:`optparse` removes it, leaving this help text::
Options:
- [...]
+ ...
-n, --noisy be noisy
--dry-run new dry-run option
if parser.values.b:
raise OptionValueError("can't use -a after -b")
parser.values.a = 1
- [...]
+ ...
parser.add_option("-a", action="callback", callback=check_order)
parser.add_option("-b", action="store_true", dest="b")
if parser.values.b:
raise OptionValueError("can't use %s after -b" % opt_str)
setattr(parser.values, option.dest, 1)
- [...]
+ ...
parser.add_option("-a", action="callback", callback=check_order, dest='a')
parser.add_option("-b", action="store_true", dest="b")
parser.add_option("-c", action="callback", callback=check_order, dest='c')
raise OptionValueError("%s option invalid when moon is full"
% opt_str)
setattr(parser.values, option.dest, 1)
- [...]
+ ...
parser.add_option("--foo",
action="callback", callback=check_moon, dest="foo")
def store_value(option, opt_str, value, parser):
setattr(parser.values, option.dest, value)
- [...]
+ ...
parser.add_option("--foo",
action="callback", callback=store_value,
type="int", nargs=3, dest="foo")
del parser.rargs[:len(value)]
setattr(parser.values, option.dest, value)
- [...]
- parser.add_option("-c", "--callback", dest="vararg_attr",
- action="callback", callback=vararg_callback)
+ ...
+ parser.add_option("-c", "--callback", dest="vararg_attr",
+ action="callback", callback=vararg_callback)
.. _optparse-extending-optparse:
For example::
- >>> re.match("c", "abcdef") # No match
- >>> re.search("c", "abcdef") # Match
+ >>> re.match("c", "abcdef") # No match
+ >>> re.search("c", "abcdef") # Match
<_sre.SRE_Match object at ...>
Regular expressions beginning with ``'^'`` can be used with :func:`search` to
restrict the match at the beginning of the string::
- >>> re.match("c", "abcdef") # No match
- >>> re.search("^c", "abcdef") # No match
+ >>> re.match("c", "abcdef") # No match
+ >>> re.search("^c", "abcdef") # No match
>>> re.search("^a", "abcdef") # Match
<_sre.SRE_Match object at ...>
in each word of a sentence except for the first and last characters::
>>> def repl(m):
- ... inner_word = list(m.group(2))
- ... random.shuffle(inner_word)
- ... return m.group(1) + "".join(inner_word) + m.group(3)
+ ... inner_word = list(m.group(2))
+ ... random.shuffle(inner_word)
+ ... return m.group(1) + "".join(inner_word) + m.group(3)
>>> text = "Professor Abdolmalek, please report your absences promptly."
>>> re.sub(r"(\w)(\w+)(\w)", repl, text)
'Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.'
except ImportError:
pass
else:
- ... # do something that requires SSL support
+ ... # do something that requires SSL support
Client-side operation
^^^^^^^^^^^^^^^^^^^^^
Some simple format string examples::
- "First, thou shalt count to {0}" # References first positional argument
- "Bring me a {}" # Implicitly references the first positional argument
- "From {} to {}" # Same as "From {0} to {1}"
- "My quest is {name}" # References keyword argument 'name'
- "Weight in tons {0.weight}" # 'weight' attribute of first positional arg
- "Units destroyed: {players[0]}" # First element of keyword argument 'players'.
+ "First, thou shalt count to {0}" # References first positional argument
+ "Bring me a {}" # Implicitly references the first positional argument
+ "From {} to {}" # Same as "From {0} to {1}"
+ "My quest is {name}" # References keyword argument 'name'
+ "Weight in tons {0.weight}" # 'weight' attribute of first positional arg
+ "Units destroyed: {players[0]}" # First element of keyword argument 'players'.
The *conversion* field causes a type coercion before formatting. Normally, the
job of formatting a value is done by the :meth:`__format__` method of the value
print "hello, world"
t = Timer(30.0, hello)
- t.start() # after 30 seconds, "hello, world" will be printed
+ t.start() # after 30 seconds, "hello, world" will be printed
.. class:: Timer(interval, function, args=[], kwargs={})
class TestStringMethods(unittest.TestCase):
- def test_upper(self):
- self.assertEqual('foo'.upper(), 'FOO')
-
- def test_isupper(self):
- self.assertTrue('FOO'.isupper())
- self.assertFalse('Foo'.isupper())
-
- def test_split(self):
- s = 'hello world'
- self.assertEqual(s.split(), ['hello', 'world'])
- # check that s.split fails when the separator is not a string
- with self.assertRaises(TypeError):
- s.split(2)
+ def test_upper(self):
+ self.assertEqual('foo'.upper(), 'FOO')
+
+ def test_isupper(self):
+ self.assertTrue('FOO'.isupper())
+ self.assertFalse('Foo'.isupper())
+
+ def test_split(self):
+ s = 'hello world'
+ self.assertEqual(s.split(), ['hello', 'world'])
+ # check that s.split fails when the separator is not a string
+ with self.assertRaises(TypeError):
+ s.split(2)
if __name__ == '__main__':
unittest.main()
# Our callable object which is intentionally not compliant to the
# standard, so the validator is going to break
def simple_app(environ, start_response):
- status = '200 OK' # HTTP Status
- headers = [('Content-type', 'text/plain')] # HTTP Headers
+ status = '200 OK' # HTTP Status
+ headers = [('Content-type', 'text/plain')] # HTTP Headers
start_response(status, headers)
# This is going to break because we need to return a list, and
# is a dictionary containing CGI-style envrironment variables and the
# second variable is the callable object (see PEP 333).
def hello_world_app(environ, start_response):
- status = '200 OK' # HTTP Status
- headers = [('Content-type', 'text/plain')] # HTTP Headers
+ status = '200 OK' # HTTP Status
+ headers = [('Content-type', 'text/plain')] # HTTP Headers
start_response(status, headers)
# The returned object is going to be printed
from xml.dom.minidom import parse, parseString
- dom1 = parse('c:\\temp\\mydata.xml') # parse an XML file by name
+ dom1 = parse('c:\\temp\\mydata.xml') # parse an XML file by name
datasource = open('c:\\temp\\mydata.xml')
- dom2 = parse(datasource) # parse an open file
+ dom2 = parse(datasource) # parse an open file
dom3 = parseString('<myxml>Some data<empty/> some more data</myxml>')
It also has children nodes over which we can iterate::
>>> for child in root:
- ... print child.tag, child.attrib
+ ... print child.tag, child.attrib
...
country {'name': 'Liechtenstein'}
country {'name': 'Singapore'}
:meth:`Element.iter`::
>>> for neighbor in root.iter('neighbor'):
- ... print neighbor.attrib
+ ... print neighbor.attrib
...
{'name': 'Austria', 'direction': 'E'}
{'name': 'Switzerland', 'direction': 'W'}
content. :meth:`Element.get` accesses the element's attributes::
>>> for country in root.findall('country'):
- ... rank = country.find('rank').text
- ... name = country.get('name')
- ... print name, rank
+ ... rank = country.find('rank').text
+ ... name = country.get('name')
+ ... print name, rank
...
Liechtenstein 1
Singapore 4
attribute to the rank element::
>>> for rank in root.iter('rank'):
- ... new_rank = int(rank.text) + 1
- ... rank.text = str(new_rank)
- ... rank.set('updated', 'yes')
+ ... new_rank = int(rank.text) + 1
+ ... rank.text = str(new_rank)
+ ... rank.set('updated', 'yes')
...
>>> tree.write('output.xml')
remove all countries with a rank higher than 50::
>>> for country in root.findall('country'):
- ... rank = int(country.find('rank').text)
- ... if rank > 50:
- ... root.remove(country)
+ ... rank = int(country.find('rank').text)
+ ... if rank > 50:
+ ... root.remove(country)
...
>>> tree.write('output.xml')
[<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
>>> for i in links: # Iterates through all found links
... i.attrib["target"] = "blank"
+ ...
>>> tree.write("output.xhtml")
.. _elementtree-qname-objects:
from SimpleXMLRPCServer import SimpleXMLRPCServer
def is_even(n):
- return n%2 == 0
+ return n % 2 == 0
server = SimpleXMLRPCServer(("localhost", 8000))
print "Listening on port 8000..."
# A marshalling error is going to occur because we're returning a
# complex number
- def add(x,y):
+ def add(x, y):
return x+y+0j
server = SimpleXMLRPCServer(("localhost", 8000))
class ProxiedTransport(xmlrpclib.Transport):
def set_proxy(self, proxy):
self.proxy = proxy
+
def make_connection(self, host):
self.realhost = host
h = httplib.HTTPConnection(self.proxy)
return h
+
def send_request(self, connection, handler, request_body):
connection.putrequest("POST", 'http://%s%s' % (self.realhost, handler))
+
def send_host(self, connection, host):
connection.putheader('Host', self.realhost)
(and the ``**expression`` argument, if any -- see below). So::
>>> def f(a, b):
- ... print a, b
+ ... print a, b
...
>>> f(b=1, *(2,))
2 1
The simple form, ``assert expression``, is equivalent to ::
if __debug__:
- if not expression: raise AssertionError
+ if not expression: raise AssertionError
The extended form, ``assert expression1, expression2``, is equivalent to ::
if __debug__:
- if not expression1: raise AssertionError(expression2)
+ if not expression1: raise AssertionError(expression2)
.. index::
single: __debug__
filename = os.environ.get('PYTHONSTARTUP')
if filename and os.path.isfile(filename):
with open(filename) as fobj:
- startup_file = fobj.read()
+ startup_file = fobj.read()
exec(startup_file)
class MyClass:
"""A simple example class"""
i = 12345
+
def f(self):
return 'hello world'
class C:
f = f1
+
def g(self):
return 'hello world'
+
h = g
Now ``f``, ``g`` and ``h`` are all attributes of class :class:`C` that refer to
class Bag:
def __init__(self):
self.data = []
+
def add(self, x):
self.data.append(x)
+
def addtwice(self, x):
self.add(x)
self.add(x)
class Employee:
pass
- john = Employee() # Create an empty employee record
+ john = Employee() # Create an empty employee record
# Fill the fields of the record
john.name = 'John Doe'
def __init__(self, data):
self.data = data
self.index = len(data)
+
def __iter__(self):
return self
+
def next(self):
if self.index == 0:
raise StopIteration
It is simple to write a function that returns a list of the numbers of the
Fibonacci series, instead of printing it::
- >>> def fib2(n): # return Fibonacci series up to n
+ >>> def fib2(n): # return Fibonacci series up to n
... """Return a list containing the Fibonacci series up to n."""
... result = []
... a, b = 0, 1
attributes to it as desired. ::
>>> try:
- ... raise Exception('spam', 'eggs')
+ ... raise Exception('spam', 'eggs')
... except Exception as inst:
- ... print type(inst) # the exception instance
- ... print inst.args # arguments stored in .args
- ... print inst # __str__ allows args to be printed directly
- ... x, y = inst.args
- ... print 'x =', x
- ... print 'y =', y
+ ... print type(inst) # the exception instance
+ ... print inst.args # arguments stored in .args
+ ... print inst # __str__ allows args to be printed directly
+ ... x, y = inst.args
+ ... print 'x =', x
+ ... print 'y =', y
...
<type 'exceptions.Exception'>
('spam', 'eggs')
>>> f = open('workfile', 'r+')
>>> f.write('0123456789abcdef')
- >>> f.seek(5) # Go to the 6th byte in the file
+ >>> f.seek(5) # Go to the 6th byte in the file
>>> f.read(1)
'5'
- >>> f.seek(-3, 2) # Go to the 3rd byte before the end
+ >>> f.seek(-3, 2) # Go to the 3rd byte before the end
>>> f.read(1)
'd'
This feature is particularly useful when you want to break long strings::
>>> text = ('Put several strings within parentheses '
- 'to have them joined together.')
+ ... 'to have them joined together.')
>>> text
'Put several strings within parentheses to have them joined together.'
Slice indices have useful defaults; an omitted first index defaults to zero, an
omitted second index defaults to the size of the string being sliced. ::
- >>> word[:2] # character from the beginning to position 2 (excluded)
+ >>> word[:2] # character from the beginning to position 2 (excluded)
'Py'
- >>> word[4:] # characters from position 4 (included) to the end
+ >>> word[4:] # characters from position 4 (included) to the end
'on'
- >>> word[-2:] # characters from the second-last (included) to the end
+ >>> word[-2:] # characters from the second-last (included) to the end
'on'
One way to remember how slices work is to think of the indices as pointing
print b,
a, b = b, a+b
- def fib2(n): # return Fibonacci series up to n
+ def fib2(n): # return Fibonacci series up to n
result = []
a, b = 0, 1
while b < n:
with self.assertRaises(TypeError):
average(20, 30, 70)
- unittest.main() # Calling from the command line invokes all tests
+ unittest.main() # Calling from the command line invokes all tests
.. _tut-batteries-included:
threading.Thread.__init__(self)
self.infile = infile
self.outfile = outfile
+
def run(self):
f = zipfile.ZipFile(self.outfile, 'w', zipfile.ZIP_DEFLATED)
f.write(self.infile)
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