Python Startup Time — Unofficial Python Development (Victor's notes) documentation (original) (raw)

CPython startup is “slow”: takes between 8 ms and 100 ms depending on the Python version, the operating system, how many .pth files are installed, if Python runs into a virtual environment, etc.

See: https://github.com/bdrung/startup-time

Raw benchmark¶

Benchmark:

python3 -m perf command -o python2.json -- python2 -c pass python3 -m perf command -o python3.json -- python3 -c pass python3 -m perf command -o python2_nosite.json -- python2 -S -c pass python3 -m perf command -o python3_nosite.json -- python3 -S -c pass

Result speed.python.org (July 2017), fatest to slowest:

• git --version: 974 us +- 7 us
• perl -e ' ': 1.18 ms +- 0.01 ms
• Python 2.7: 6.4 ms with site; 3.0 ms without site (-S)
• php -r ' ': 8.57 ms +- 0.05 ms
• Python 3.7: 14.5 ms with site; 8.4 ms without site (-S)
• ruby -e ' ': 32.8 ms +- 0.1 ms
• hg version: 44.6 ms +- 0.2 ms

Reference: benchmark run at July 2017.

importtime¶

To analyze the startup time of your application, Python 3.7 and newer have a builtin profiler on import time: -X importtime option.

Truncated example:

$ python3.7 -X importtime -c pass import time: self [us] | cumulative | imported package import time: 274 | 274 | zipimport (...) import time: 949 | 2055 | io import time: 453 | 453 | _stat import time: 701 | 1154 | stat import time: 595 | 595 | genericpath import time: 886 | 1480 | posixpath import time: 3005 | 3005 | _collections_abc import time: 1922 | 7559 | os (...) import time: 4325 | 22832 | site

An alternative is to set PYTHONPROFILEIMPORTTIME=1 environment variable.

No surprise, site has the longest cumulative time. Disable site to speedup Python :-) Example:

$ python3.7 -X importtime -S -c pass import time: self [us] | cumulative | imported package import time: 88 | 88 | zipimport import time: 580 | 580 | _frozen_importlib_external import time: 66 | 66 | _codecs import time: 498 | 564 | codecs import time: 411 | 411 | encodings.aliases import time: 678 | 1653 | encodings import time: 232 | 232 | encodings.utf_8 import time: 155 | 155 | _signal import time: 341 | 341 | encodings.latin_1 import time: 56 | 56 | _abc import time: 273 | 329 | abc import time: 298 | 626 | io

tuna is a Python profile viewer which accepts importtime logs as input, see Nico Schlömer’s comment on bpo-31415. Extract:

python -X importprofile application.py 2>import.log tuna import.log

Example with python3.7 -X importtime -c pass:

Links:

• How to speed up Python application startup time(Jan, 2018) by INADA Naoki.
• importtime-waterfall (GitHub project): Generate waterfalls from -X importtime tracing.

See also Python Import.

.pth files¶

See Deprecate and remove pth filescreated by Barry A. Warsaw at 2018-06-22.

Links¶

• python-dev: Python startup time (July 2017) by Victor Stinner
• LWN: Reducing Python’s startup time(August 16, 2017) by Jake Edge.