From 579644ade04cdba3d0fdabe84b55b51e2ed64b45 Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Sat, 27 Jan 2024 16:19:27 -0800
Subject: [PATCH 1/3] gh-109653: Improve import time of importlib.metadata /
 email.utils
MIME-Version: 1.0
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My criterion for delayed imports is that they're only worth it if the
majority of users of the module would benefit from it, otherwise you're
just moving latency around unpredictably.

mktime_tz is not used anywhere in the standard library and grep.app
indicates it's not got much use in the ecosystem either.

Distribution.files is not nearly as widely used as other
importlib.metadata APIs, so we defer the csv import.

Before:
```
λ hyperfine -w 8 './python -c "import importlib.metadata"'
Benchmark 1: ./python -c "import importlib.metadata"
  Time (mean ± σ):      65.1 ms ±   0.5 ms    [User: 55.3 ms, System: 9.8 ms]
  Range (min … max):    64.4 ms …  66.4 ms    44 runs
```

After:
```
λ hyperfine -w 8 './python -c "import importlib.metadata"'
Benchmark 1: ./python -c "import importlib.metadata"
  Time (mean ± σ):      62.0 ms ±   0.3 ms    [User: 52.5 ms, System: 9.6 ms]
  Range (min … max):    61.3 ms …  62.8 ms    46 runs
```

for about a 3ms saving with warm disk cache, maybe 7-11ms with cold disk
cache.
---
 Lib/email/_parseaddr.py            | 4 +++-
 Lib/importlib/metadata/__init__.py | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Lib/email/_parseaddr.py b/Lib/email/_parseaddr.py
index febe411355d6be..96f0a340e7df10 100644
--- a/Lib/email/_parseaddr.py
+++ b/Lib/email/_parseaddr.py
@@ -13,7 +13,7 @@
     'quote',
     ]
 
-import time, calendar
+import time
 
 SPACE = ' '
 EMPTYSTRING = ''
@@ -194,6 +194,8 @@ def mktime_tz(data):
         # No zone info, so localtime is better assumption than GMT
         return time.mktime(data[:8] + (-1,))
     else:
+        import calendar
+
         t = calendar.timegm(data)
         return t - data[9]
 
diff --git a/Lib/importlib/metadata/__init__.py b/Lib/importlib/metadata/__init__.py
index 7b142e786e829e..69f41eb33cf287 100644
--- a/Lib/importlib/metadata/__init__.py
+++ b/Lib/importlib/metadata/__init__.py
@@ -1,7 +1,6 @@
 import os
 import re
 import abc
-import csv
 import sys
 import json
 import email
@@ -478,6 +477,8 @@ def make_file(name, hash=None, size_str=None):
 
         @pass_none
         def make_files(lines):
+            import csv
+
             return starmap(make_file, csv.reader(lines))
 
         @pass_none

From 94fd0d728226fe8484a9b8e658893bcb5028f479 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Sun, 28 Jan 2024 00:48:15 +0000
Subject: [PATCH 2/3] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
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---
 .../next/Library/2024-01-28-00-48-12.gh-issue-109653.vF4exe.rst  | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2024-01-28-00-48-12.gh-issue-109653.vF4exe.rst

diff --git a/Misc/NEWS.d/next/Library/2024-01-28-00-48-12.gh-issue-109653.vF4exe.rst b/Misc/NEWS.d/next/Library/2024-01-28-00-48-12.gh-issue-109653.vF4exe.rst
new file mode 100644
index 00000000000000..fb3382098853b3
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-01-28-00-48-12.gh-issue-109653.vF4exe.rst
@@ -0,0 +1 @@
+Improve import time of :mod:`importlib.metadata` and :mod:`email.utils`.

From 3eefd3247086c86a2a12e174f2cfd4386579a47c Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Sun, 28 Jan 2024 01:49:51 -0800
Subject: [PATCH 3/3] comments

---
 Lib/email/_parseaddr.py            | 1 +
 Lib/importlib/metadata/__init__.py | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/Lib/email/_parseaddr.py b/Lib/email/_parseaddr.py
index 96f0a340e7df10..0f1bf8e4253ec4 100644
--- a/Lib/email/_parseaddr.py
+++ b/Lib/email/_parseaddr.py
@@ -194,6 +194,7 @@ def mktime_tz(data):
         # No zone info, so localtime is better assumption than GMT
         return time.mktime(data[:8] + (-1,))
     else:
+        # Delay the import, since mktime_tz is rarely used
         import calendar
 
         t = calendar.timegm(data)
diff --git a/Lib/importlib/metadata/__init__.py b/Lib/importlib/metadata/__init__.py
index 69f41eb33cf287..c612fbefee2e80 100644
--- a/Lib/importlib/metadata/__init__.py
+++ b/Lib/importlib/metadata/__init__.py
@@ -477,6 +477,8 @@ def make_file(name, hash=None, size_str=None):
 
         @pass_none
         def make_files(lines):
+            # Delay csv import, since Distribution.files is not as widely used
+            # as other parts of importlib.metadata
             import csv
 
             return starmap(make_file, csv.reader(lines))