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Have a CLI Python application?

Want to automate testing of the actual console input & outputof your user-facing components?

stdio Manager can help.

While some functionality here is more or less duplicative ofredirect_stdout andredirect_stderr incontextlibwithin the standard library,it provides (i) a much more concise way to mock bothstdout andstderr at the same time,and (ii) a mechanism for mockingstdin, which is not available incontextlib.

First, install:

$ pip install stdio-mgr

Then use!

All of the below examples assumestdio_mgr has alreadybeen imported via:

>>> from stdio_mgr import stdio_mgr

Mockstdout:

>>> with stdio_mgr() as (in_, out_, err_):...     print('foobar')...     out_cap = out_.getvalue().replace(os.linesep, '\n')>>> out_cap'foobar\n'>>> in_.closed and out_.closed and err_.closedTrue

By defaultprintappends a newlineafter each argument, which is whyout_cap is'foobar\n'and not just'foobar'.

As currently implemented,stdio_mgr closes all three mocked streamsupon exiting the managed context.

Mockstderr:

>>> import warnings>>> with stdio_mgr() as (in_, out_, err_):...     warnings.warn("foo has no bar")...     err_cap = err_.getvalue().replace(os.linesep, '\n')>>> err_cap'...UserWarning: foo has no bar\n...'

Mockstdin:

The simulated user input has to be pre-loaded to the mocked stream.Be sure to include newlines in the input to correspond toeach mocked Enterkeypress!Otherwise,input will hang, waiting for a newlinethat will never come.

If the entirety of the input is known in advance,it can just be provided as an argument tostdio_mgr.Otherwise,.append() mocked input toin_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().replace(os.linesep, '\n')>>> in_cap'foobar'>>> in_cap2'foo'>>> out_cap'baz\n??? foobar\n??? foo\n'

The_ = assignment suppressesprinting of the return valuefrom thein_.append() call--otherwise, it would be interleavedinout_cap, since this example is shown for an interactive context.For non-interactive execution, as withunittest,pytest, etc.,these 'muting' assignments should not be necessary.

Both the'??? ' prompts forinputand the mocked input stringsare echoed toout_, mimicking what a CLI user would see.

A subtlety: While the trailing newline on, e.g.,'foobar\n' is strippedbyinput, it isretained inout_.This is becausein_ tees the content read from it toout_before that content is passed toinput.

Want to modify internalprintcallswithin a function or method?

In addition to mocking,stdio_mgr can also be used towrap functions that directly output tostdout/stderr. Astdout 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 onPyPI(pip install stdio-mgr).

Source onGitHub. Bug reportsand feature requests are welcomed at theIssues page there.

Copyright (c) 2018-2019 Brian Skinn

License: The MIT License. SeeLICENSE.txtfor full license terms.