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pythonformattingf-string

Define a triple-quoted f-string with newline-containing substrings inside a function without outputted indents


I'm trying to pretty-print a HTTP request (that I've mocked here).

from typing import NamedTuple

class RequestMock(NamedTuple):
    method = 'POST'
    url = 'https://bob.com'
    body = 'body1\nbody2'
    headers = {'a': '1', 'b': '2'}

I have a function that does this:

req = RequestMock()

def print1(req):
    headers = '\n'.join(f'{k}: {v}' for k, v in req.headers.items())
    s = '\n'.join([
        f'{req.method} {req.url}',
        headers,
        req.body
    ])
    print(s)

print1(req)
# POST https://bob.com
# a: 1
# b: 2
# body1
# body2

But when I've tried to rewrite it with f-strings for clarity and ease of modification, I get some bad indents:

# what I want the code to look like
def print2(req):
    headers = '\n'.join(f'{k}: {v}' for k, v in req.headers.items())
    s = f"""
    {req.method} {req.url}
    {headers}
    {req.body}
    """
    print(s)

print2(req)
#     POST https://bob.com
#     a: 1
# b: 2
#     body1
# body2

I know this is because I'm defining strings with newlines and putting them in a triple-quoted string. Is there a simple way to get the output I'm looking with a triple-quoted f-string defined in a function and without having to know the indentation level of its definition? I've played with textwrap.indent, textwrap.dedent, str.lstrip, re, etc., but the code stops being simple and pythonic fast. The closest thing I've come up with is the following, but the length is awkward and I feel like I'm repeating myself.

def print3(req):
    headers = '\n'.join(f'{k}: {v}' for k, v in req.headers.items())
    s = textwrap.dedent("""
    {method} {url}
    {headers}
    {body}
    """).strip()
    s = s.format(
        method=req.method,
        url=req.url,
        headers=headers,
        body=req.body,
    )
    print(s)
print3(req)
# POST https://bob.com
# a: 1
# b: 2
# body1
# body2

Solution

  • I think you can try to take advantage of implicit string concatenation for a semi-nice looking solution:

    def print4(req):
        headers = '\n'.join(f'{k}: {v}' for k, v in req.headers.items())
        s = (f'{req.method} {req.url}\n'
             f'{headers}\n'
             f'{req.body}')
        print(s)
    
    print4(req)
    

    Output:

    POST https://bob.com
    a: 1
    b: 2
    body1
    body2
    

    Note that, if you want, you can take out the parentheses and use backslashes:

    s = f'{req.method} {req.url}\n' \
        f'{headers}\n'              \
        f'{req.body}'
    

    However, the style guide prefers parentheses over backslashes.


    Another option:

    def print5(req):
        headers = '\n'.join(f'{k}: {v}' for k, v in req.headers.items())
        s = f"""
        {req.method} {req.url}
        {headers}
        {req.body}
        """
        s = '\n'.join(l.lstrip() for l in s.splitlines())
        print(s)