statement looks for a top-level module with the given name.
When packages are structured into subpackages (as with the
-\module{sound} package in the example), there's no shortcut to refer
-to submodules of sibling packages - the full name of the subpackage
-must be used. For example, if the module
-\module{sound.filters.vocoder} needs to use the \module{echo} module
-in the \module{sound.effects} package, it can use \code{from
-sound.effects import echo}.
+\module{sound} package in the example), you can use absolute
+imports to refer to submodules of siblings packages.
+For example, if the module \module{sound.filters.vocoder} needs to
+use the \module{echo} module in the \module{sound.effects} package,
+it can use \code{from sound.effects import echo}.
Starting with Python 2.5, in addition to the implicit relative imports
-described above, you can write explicit relative imports with the
+described above, you can also write explicit relative imports with the
\code{from module import name} form of import statement. These explicit
relative imports use leading dots to indicate the current and parent
packages involved in the relative import. From the \module{surround}
--- /dev/null
+
+doctests = """
+
+ >>> k = "old value"
+ >>> { k: None for k in range(10) }
+ {0: None, 1: None, 2: None, 3: None, 4: None, 5: None, 6: None, 7: None, 8: None, 9: None}
+ >>> k
+ 'old value'
+
+ >>> { k: k+10 for k in range(10) }
+ {0: 10, 1: 11, 2: 12, 3: 13, 4: 14, 5: 15, 6: 16, 7: 17, 8: 18, 9: 19}
+
+ >>> g = "Global variable"
+ >>> { k: g for k in range(10) }
+ {0: 'Global variable', 1: 'Global variable', 2: 'Global variable', 3: 'Global variable', 4: 'Global variable', 5: 'Global variable', 6: 'Global variable', 7: 'Global variable', 8: 'Global variable', 9: 'Global variable'}
+
+ >>> { k: v for k in range(10) for v in range(10) if k == v }
+ {0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}
+
+ >>> { k: v for v in range(10) for k in range(v*9, v*10) }
+ {9: 1, 18: 2, 19: 2, 27: 3, 28: 3, 29: 3, 36: 4, 37: 4, 38: 4, 39: 4, 45: 5, 46: 5, 47: 5, 48: 5, 49: 5, 54: 6, 55: 6, 56: 6, 57: 6, 58: 6, 59: 6, 63: 7, 64: 7, 65: 7, 66: 7, 67: 7, 68: 7, 69: 7, 72: 8, 73: 8, 74: 8, 75: 8, 76: 8, 77: 8, 78: 8, 79: 8, 81: 9, 82: 9, 83: 9, 84: 9, 85: 9, 86: 9, 87: 9, 88: 9, 89: 9}
+
+ >>> { x: y for y, x in ((1, 2), (3, 4)) } = 5 # doctest: +IGNORE_EXCEPTION_DETAIL
+ Traceback (most recent call last):
+ ...
+ SyntaxError: ...
+
+ >>> { x: y for y, x in ((1, 2), (3, 4)) } += 5 # doctest: +IGNORE_EXCEPTION_DETAIL
+ Traceback (most recent call last):
+ ...
+ SyntaxError: ...
+
+"""
+
+__test__ = {'doctests' : doctests}
+
+def test_main(verbose=None):
+ import sys
+ from test import test_support
+ from test import test_dictcomps
+ test_support.run_doctest(test_dictcomps, verbose)
+
+ # verify reference counting
+ if verbose and hasattr(sys, "gettotalrefcount"):
+ import gc
+ counts = [None] * 5
+ for i in range(len(counts)):
+ test_support.run_doctest(test_dictcomps, verbose)
+ gc.collect()
+ counts[i] = sys.gettotalrefcount()
+ print(counts)
+
+if __name__ == "__main__":
+ test_main(verbose=True)
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