How can I print literal curly-brace characters in python string and also use .format on it?

Question

x = \" \\{ Hello \\} {0} \"
print(x.format(42))

gives me : Key Error: Hello\\\\

I want to print the output: {Hello} 42

Answer 1

If you want to only print one curly brace (for example {) you can use {{, and you can add more braces later in the string if you want. For example:

>>> f'{{ there is a curly brace on the left. Oh, and 1 + 1 is {1 + 1}'
'{ there is a curly brace on the left. Oh, and 1 + 1 is 2'

Answer 2

You need to double the {{ and }}:

>>> x = " {{ Hello }} {0} "
>>> print(x.format(42))
' { Hello } 42 '

Here's the relevant part of the Python documentation for format string syntax:

Format strings contain “replacement fields” surrounded by curly braces {}. Anything that is not contained in braces is considered literal text, which is copied unchanged to the output. If you need to include a brace character in the literal text, it can be escaped by doubling: {{ and }}.

Answer 3

You can do this by using raw string method by simply adding character 'r' without quotes before the string.

# to print '{I am inside braces}'
print(r'{I am inside braces}')

Answer 4

Try doing this:

x = " {{ Hello }} {0} "
print x.format(42)

Answer 5

Use escape sequences to escape the curly braces in the f-string. Ex:print(f'{a={1}}')

Answer 6

I recently ran into this, because I wanted to inject strings into preformatted JSON. My solution was to create a helper method, like this:

def preformat(msg):
    """ allow {{key}} to be used for formatting in text
    that already uses curly braces.  First switch this into
    something else, replace curlies with double curlies, and then
    switch back to regular braces
    """
    msg = msg.replace('{{', '<<<').replace('}}', '>>>')
    msg = msg.replace('{', '{{').replace('}', '}}')
    msg = msg.replace('<<<', '{').replace('>>>', '}')
    return msg

You can then do something like:

formatted = preformat("""
    {
        "foo": "{{bar}}"
    }""").format(bar="gas")

Gets the job done if performance is not an issue.