#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 66b2fb4..04fc0f2 100644
--- a/Doc/library/csv.rst
+++ b/Doc/library/csv.rst
@@ -167,7 +167,11 @@
.. 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 @@
.. 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