[New-bugs-announce] [issue30152] Reduce the number of imports for argparse

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

Since argparse becomes more used as standard way of parsing command-line arguments, the number of imports involved when import argparse becomes more important. Proposed patch reduces that number by 10 modules.

Unpatched:

$ ./python -c 'import sys; s = set(sys.modules); import argparse; print(len(s), len(sys.modules), len(set(sys.modules) - s)); print(sorted(set(sys.modules) - s))'
35 65 30
['_collections', '_functools', '_heapq', '_locale', '_operator', '_sre', '_struct', 'argparse', 'collections', 'collections.abc', 'copy', 'copyreg', 'enum', 'functools', 'gettext', 'heapq', 'itertools', 'keyword', 'locale', 'operator', 're', 'reprlib', 'sre_compile', 'sre_constants', 'sre_parse', 'struct', 'textwrap', 'types', 'warnings', 'weakref']

$ ./python -S -c 'import sys; s = set(sys.modules); import argparse; print(len(s), len(sys.modules), len(set(sys.modules) - s)); print(sorted(set(sys.modules) - s))'
23 61 38
['_collections', '_collections_abc', '_functools', '_heapq', '_locale', '_operator', '_sre', '_stat', '_struct', 'argparse', 'collections', 'collections.abc', 'copy', 'copyreg', 'enum', 'errno', 'functools', 'genericpath', 'gettext', 'heapq', 'itertools', 'keyword', 'locale', 'operator', 'os', 'os.path', 'posixpath', 're', 'reprlib', 'sre_compile', 'sre_constants', 'sre_parse', 'stat', 'struct', 'textwrap', 'types', 'warnings', 'weakref']

Patched:

$ ./python -c 'import sys; s = set(sys.modules); import argparse; print(len(s), len(sys.modules), len(set(sys.modules) - s)); print(sorted(set(sys.modules) - s))'
35 55 20
['_collections', '_functools', '_locale', '_operator', '_sre', 'argparse', 'collections', 'copyreg', 'enum', 'functools', 'itertools', 'keyword', 'operator', 're', 'reprlib', 'sre_compile', 'sre_constants', 'sre_parse', 'types', 'weakref']

$ ./python -S -c 'import sys; s = set(sys.modules); import argparse; print(len(s), len(sys.modules), len(set(sys.modules) - s)); print(sorted(set(sys.modules) - s))'
23 51 28
['_collections', '_collections_abc', '_functools', '_locale', '_operator', '_sre', '_stat', 'argparse', 'collections', 'copyreg', 'enum', 'errno', 'functools', 'genericpath', 'itertools', 'keyword', 'operator', 'os', 'os.path', 'posixpath', 're', 'reprlib', 'sre_compile', 'sre_constants', 'sre_parse', 'stat', 'types', 'weakref']

The patch defers importing rarely used modules. For example textwrap and gettext are used only for output a help and error messages.

The patch also makes argparse itself be imported only when the module is used as a script, not just imported. The patch also replaces importing collections.abc with _collections_abc in some other basic modules (like pathlib), this could allow to avoid importing the collections package if it is not used.

Unavoided imports:

* functools is used in re for decorating _compile_repl with lru_cache.
* collections is used in functools for making CacheInfo a named tuple.
* enum is used in re for creating RegexFlag.
* types is used in enum for decorating some properties with DynamicClassAttribute.

----------
components: Library (Lib)
messages: 292200
nosy: bethard, haypo, rhettinger, serhiy.storchaka
priority: normal
severity: normal
stage: patch review
status: open
title: Reduce the number of imports for argparse
type: enhancement
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30152>
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