#20628: make it clear that DictReader/Writer *fieldnames* is a Sequence.

Patch by Sean Rodman.

diff --git a/Doc/library/csv.rst b/Doc/library/csv.rst
index 66b2fb4e09b676185d6ae7fa964437949142392e..04fc0f28ca1b762a54db68fa37938302d4c665ce 100644 (file)
--- a/Doc/library/csv.rst
+++ b/Doc/library/csv.rst
@@ -167,7 +167,11 @@ The :mod:`csv` module defines the following classes:
 .. class:: DictReader(csvfile, fieldnames=None, restkey=None, restval=None, dialect='excel', *args, **kwds)
 
    Create an object which operates like a regular reader but maps the information
-   read into a dict whose keys are given by the optional  *fieldnames* parameter.
+   read into a dict whose keys are given by the optional *fieldnames*
+   parameter.  The *fieldnames* parameter is a :ref:`sequence
+   <collections-abstract-base-classes>` whose elements are associated with the
+   fields of the input data in order. These elements become the keys of the
+   resulting dictionary.
    If the *fieldnames* parameter is omitted, the values in the first row of the
    *csvfile* will be used as the fieldnames.  If the row read has more fields
    than the fieldnames sequence, the remaining data is added as a sequence
@@ -180,7 +184,9 @@ The :mod:`csv` module defines the following classes:
 .. class:: DictWriter(csvfile, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)
 
    Create an object which operates like a regular writer but maps dictionaries onto
-   output rows.  The *fieldnames* parameter identifies the order in which values in
+   output rows.  The *fieldnames* parameter is a :ref:`sequence
+   <collections-abstract-base-classes>` of keys that identify the order in
+   which values in
    the dictionary passed to the :meth:`writerow` method are written to the
    *csvfile*.  The optional *restval* parameter specifies the value to be written
    if the dictionary is missing a key in *fieldnames*.  If the dictionary passed to