libfaketime 0.4.0

A fast alternative to freezegun that wraps libfaketime.

python-libfaketime: fast date/time mocking

python-libfaketime is a wrapper of libfaketime for python.

import datetime

from libfaketime import fake_time, reexec_if_needed

# libfaketime needs to be preloaded by the dynamic linker.
# This will exec the same command, but with the proper environment variables set.
# You can also skip this and manually manage your env (see "How to avoid re-exec").
reexec_if_needed()

def get_tomorrow():
    return datetime.date.today() + datetime.timedelta(days=1)


@fake_time('2014-01-01 00:00:00')
def test_get_tomorrow():
    assert get_tomorrow() == datetime.date(2014, 1, 2)

It serves as a fast drop-in replacement for freezegun. Here’s the output of a totally unscientific benchmark on my laptop:

$ python benchmark.py
re-exec with libfaketime dependencies
timing 1000 executions of <class 'libfaketime.fake_time'>
0.021755 seconds

$ python benchmark.py freezegun
timing 1000 executions of <function freeze_time at 0x10aaa1140>
6.561472 seconds

Some brief details:

• linux and osx, python 2/3

• microsecond resolution

• accepts datetimes and strings that can be parsed by dateutil

• not threadsafe

• will break profiling. A workaround: use libfaketime.{begin, end}_callback to disable/enable your profiler.

To install: pip install libfaketime.

Use with py.test

It’s easiest to reexec from inside the pytest_configure hook:

# conftest.py
from libfaketime import reexec_if_needed

def pytest_configure():
    reexec_if_needed()

How to avoid re-exec

Sometimes, re-exec does unexpected things. You can avoid those problems by preloading libfaketime yourself. The environment variables you need can be found by running python-libfaketime on the command line:

$ python-libfaketime
export LD_PRELOAD="/home/foo/<snip>/vendor/libfaketime/src/libfaketime.so.1"
export FAKETIME_DID_REEXEC=true

You can use them as such:

eval $(python-libfaketime)
nosetests  # ...or any other code that imports libfaketime

Changelog

Semantic versioning is used.

0.4.0

released 2016-04-02

• freezegun’s tick() is now supported; see their docs for usage.

0.3.0

released 2016-03-04

• invoking libfaketime from the command line will now print the necessary environment to avoid a re-exec.

0.2.1

released 2016-03-01

• python 3 support

0.1.1

released 2015-09-11

• prevent distribution of test directory: https://github.com/simon-weber/python-libfaketime/pull/4

0.1.0

released 2015-06-23

• add global start/stop callbacks

0.0.3

released 2015-03-28

• initial packaged release