Question

I have a class Commit.

class Commit:
    def __init__(self, uid, message):
        self.uid = uid
        self.message = message

    def __str__(self):
        print(self.__dict__)
        return textwrap.dedent('''\
        Commit: {uid}

        {message}
        ''').format(self.__dict__)

This seems right to me; both keys exists and are non-None, as seen from the output of the print call:

{'message': 'Hello, world!', 'uid': 1}

However, the call to str.format() on the list line raises a KeyError.

Traceback (most recent call last):
  File "../Pynewood/pnw", line 7, in 
    cli(sys.argv)
  File "/Users/daknok/Desktop/Pynewood/pynewood/cli.py", line 11, in cli
    print(commit)
  File "/Users/daknok/Desktop/Pynewood/pynewood/commit.py", line 14, in __str__
    ''').format(self.__dict__)
KeyError: 'uid'

Why am I getting this error, while the keys clearly exist in the dictionary?

Answer 1

str.format() expects kwargs, so you need to expand the dictionary using **.

def __str__(self):
    return textwrap.dedent('''\
    Commit: {uid}

    {message}
    ''').format(**self.__dict__)