gh-118761: Improve import time for csv (#128858)

picnixz · web-flow · commit d5e9aa690a19 · 2025-01-18T11:45:18.000+01:00
This reduces the import time of the `csv` module by up to five times,
by importing `re` on demand.

In particular, the `re` module is no more implicitly exposed as `csv.re`.
diff --git a/Lib/csv.py b/Lib/csv.py
@@ -63,7 +63,6 @@ class excel:
         written as two quotes
 """
 
-import re
 import types
 from _csv import Error, writer, reader, register_dialect, \
                  unregister_dialect, get_dialect, list_dialects, \
@@ -281,6 +280,7 @@ def _guess_quote_and_delimiter(self, data, delimiters):
         If there is no quotechar the delimiter can't be determined
         this way.
         """
+        import re
 
         matches = []
         for restr in (r'(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?P=delim)', # ,".*?",
diff --git a/Misc/NEWS.d/next/Library/2025-01-15-09-45-43.gh-issue-118761.TvAC8E.rst b/Misc/NEWS.d/next/Library/2025-01-15-09-45-43.gh-issue-118761.TvAC8E.rst
@@ -0,0 +1,3 @@
+Reduce the import time of :mod:`csv` by up to five times, by importing
+:mod:`re` on demand. In particular, ``re`` is no more implicitly exposed
+as ``csv.re``. Patch by Bénédikt Tran.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Reduce the import time of :mod:`csv` by up to five times, by importing
	`2`	+:mod:`re` on demand. In particular, ``re`` is no more implicitly exposed
	`3`	+as ``csv.re``. Patch by Bénédikt Tran.