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Most Recent Stable Release:
Info:
Have a CLI Python application?
Want to automate testing of the actual console input & output of your user-facing components?
stdio Manager can help.
While some functionality here is more or less duplicative of
redirect_stdout
and redirect_stderr
in contextlib
within the standard library,
it provides (i) a much more concise way to mock both stdout
and stderr
at the same time,
and (ii) a mechanism for mocking stdin
, which is not available in contextlib
.
First, install:
$ pip install stdio-mgr
Then use!
All of the below examples assume stdio_mgr
has already
been imported via:
from stdio_mgr import stdio_mgr
Mock stdout
:
>>> with stdio_mgr() as (in_, out_, err_): ... print('foobar') ... out_cap = out_.getvalue() >>> out_cap 'foobar\n' >>> in_.closed and out_.closed and err_.closed True
By default print
appends a newline
after each argument, which is why out_cap
is 'foobar\n'
and not just 'foobar'
.
As currently implemented, stdio_mgr
closes all three mocked streams
upon exiting the managed context.
Mock stderr
:
>>> import warnings >>> with stdio_mgr() as (in_, out_, err_): ... warnings.warn("foo has no bar") ... err_cap = err_.getvalue() >>> err_cap '...UserWarning: foo has no bar\n...'
Mock stdin
:
The simulated user input has to be pre-loaded to the mocked stream.
Be sure to include newlines in the input to correspond to
each mocked Enter keypress!
Otherwise, input
will hang, waiting for a newline
that will never come.
If the entirety of the input is known in advance,
it can just be provided as an argument to stdio_mgr
.
Otherwise, .append()
mocked input to in_
within the managed context as needed:
>>> with stdio_mgr('foobar\n') as (in_, out_, err_): ... print('baz') ... in_cap = input('??? ') ... ... _ = in_.append(in_cap[:3] + '\n') ... in_cap2 = input('??? ') ... ... out_cap = out_.getvalue() >>> in_cap 'foobar' >>> in_cap2 'foo' >>> out_cap 'baz\n??? foobar\n??? foo\n'
The _ =
assignment suppresses print
ing of the return value
from the in_.append()
call--otherwise, it would be interleaved
in out_cap
, since this example is shown for an interactive context.
For non-interactive execution, as with unittest
, pytest
, etc.,
these 'muting' assignments should not be necessary.
Both the '??? '
prompts for input
and the mocked input strings
are echoed to out_
, mimicking what a CLI user would see.
A subtlety: While the trailing newline on, e.g., 'foobar\n'
is stripped
by input
, it is retained in out_
.
This is because in_
tees the content read from it to out_
before that content is passed to input
.
Want to modify internal print
calls
within a function or method?
In addition to mocking, stdio_mgr
can also be used to
wrap functions that directly output to stdout
/stderr
. A stdout
example:
>>> def emboxen(func): ... def func_wrapper(s): ... from stdio_mgr import stdio_mgr ... ... with stdio_mgr() as (in_, out_, err_): ... func(s) ... content = out_.getvalue() ... ... max_len = max(map(len, content.splitlines())) ... fmt_str = '| {{: <{0}}} |\n'.format(max_len) ... ... newcontent = '=' * (max_len + 4) + '\n' ... for line in content.splitlines(): ... newcontent += fmt_str.format(line) ... newcontent += '=' * (max_len + 4) ... ... print(newcontent) ... ... return func_wrapper >>> @emboxen ... def testfunc(s): ... print(s) >>> testfunc("""\ ... Foo bar baz quux. ... Lorem ipsum dolor sit amet.""") =============================== | Foo bar baz quux. | | Lorem ipsum dolor sit amet. | ===============================
Available on PyPI
(pip install stdio-mgr
).
Source on GitHub. Bug reports and feature requests are welcomed at the Issues page there.
Copyright (c) 2018-2019 Brian Skinn
License: The MIT License. See LICENSE.txt for full license terms.