https://github.com/elifiner/affirm

Improved error messages for Python assert statements
https://github.com/elifiner/affirm

Last synced: about 1 month ago
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Improved error messages for Python assert statements

• Host: GitHub
• URL: https://github.com/elifiner/affirm
• Owner: elifiner
• License: mit
• Created: 2016-06-02T19:15:29.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2016-10-30T04:14:21.000Z (almost 8 years ago)
• Last Synced: 2024-07-09T02:24:54.778Z (2 months ago)
• Language: Python
• Size: 9.77 KB
• Stars: 63
• Watchers: 3
• Forks: 1
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.md

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• starred-awesome - affirm - Improved error messages for Python assert statements (Python)

README

        
affirm

======

This small library improves Python `assert` error messages to contain more useful information.

I like to use `assert`'s liberaly thoughout my code to document my assumptions and when one of them fails, I really like to know as much as possible about what failed and why.

Installation

------------

    $ pip install affirm

Using the `assert` statement

----------------------------

Before affirm, if you run a simple script in Python:

    a = 1

    b = 2

    assert a > b

The result will be:

    Traceback (most recent call last):

      File "test.py", line 3, in 

        assert a > b

    AssertionError

We can see the traceback, but not the actuall values that caused the assert to fail, which is not very useful for debugging.

If you `import affirm` at the top of the script, like so:

    import affirm

    a = 1

    b = 2

    assert a > b

You'll get:

    Traceback (most recent call last):

      File "test.py", line 4, in 

        assert a > b

    AssertionError: assertion (a > b) failed with a=1, b=2

Which is much more useful.

Note that the standard behaviour of supplying a message with the assert statement still works:

    import affirm

    a = 1

    b = 2

    assert a > b, "something went wrong"

Will give you:

    Traceback (most recent call last):

      File "test.py", line 4, in 

        assert a > b

    AssertionError: something went wrong

Using the `affirm` function

---------------------------

There's only one problem with using the standard `assert` statement. If you catch the exception and print it yourself:

    import affirm

    a = 1

    b = 2

    try:

        assert a > b

    except Exception as e:

        print(str(e))

The result will be:

```

```

Yes, absolutely nothing. Calling `str` on `AssertionError` results in an empty string.

If you want to be able to catch the assertion errors and print the messages into e.g. log, you'll need to use the `affirm` function instead of the `assert` statement, like so:

    from affirm import affirm

    a = 1

    b = 2

    try:

        affirm(a > b)

    except Exception as e:

        print(str(e))

Now we get the expected:

    assertion (a > b) failed with a=1, b=2