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

问题

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

gives me : Key Error: Hello\\\\

I want to print the output: {Hello} 42

回答1:

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 }}.

回答2:

You escape it by doubling the braces.

Eg:

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

回答3:

The OP wrote this comment:

I was trying to format a small JSON for some purposes, like this: '{"all": false, "selected": "{}"}'.format(data) to get something like {"all": false, "selected": "1,2"}

It's pretty common that the "escaping braces" issue comes up when dealing with JSON.

I suggest doing this:

import json
data = "1,2"
mydict = {"all": "false", "selected": data}
json.dumps(mydict)

It's cleaner than the alternative, which is:

'{{"all": false, "selected": "{}"}}'.format(data)

Using the json library is definitely preferable when the JSON string gets more complicated than the example.

回答4:

Python 3.6+ (2017)

In the recent versions of Python one would use f-strings (see also PEP498).

With f-strings one should use double {{ or }}

n = 42  
print(f" {{Hello}} {n} ")

produces the desired

 {Hello} 42

If you need to resolve an expression in the brackets instead of using literal text you'll need three sets of brackets:

hello = "HELLO"
print(f"{{{hello.lower()}}}")

produces

{hello}

回答5:

Try doing this:

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

回答6:

Try this:

x = "{{ Hello }} {0}"

回答7:

Although not any better, just for the reference, you can also do this:

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

It can be useful for example when someone wants to print {argument}. It is maybe more readable than '{{{}}}'.format('argument')

Note that you omit argument positions (e.g. {} instead of {0}) after Python 2.7

回答8:

If you are going to be doing this a lot, it might be good to define a utility function that will let you use arbitrary brace substitutes instead, like

def custom_format(string, brackets, *args, **kwargs):
    if len(brackets) != 2:
        raise ValueError('Expected two brackets. Got {}.'.format(len(brackets)))
    padded = string.replace('{', '{{').replace('}', '}}')
    substituted = padded.replace(brackets[0], '{').replace(brackets[1], '}')
    formatted = substituted.format(*args, **kwargs)
    return formatted

>>> custom_format('{{[cmd]} process 1}', brackets='[]', cmd='firefox.exe')
'{{firefox.exe} process 1}'

Note that this will work either with brackets being a string of length 2 or an iterable of two strings (for multi-character delimiters).

回答9:

Reason is , {} is the syntax of .format() so in your case .format() doesn't recognize {Hello} so it threw an error.

you can override it by using double curly braces {{}},

x = " {{ Hello }} {0} "

or

try %s for text formatting,

x = " { Hello } %s"
print x%(42)  

回答10:

If you need to keep two curly braces in the string, you need 5 curly braces on each side of the variable.

>>> myvar = 'test'
>>> "{{{{{0}}}}}".format(myvar)
'{{test}}'

回答11:

I stumbled upon this problem when trying to print text, which I can copy paste into a Latex document. I extend on this answer and make use of named replacement fields:

Lets say you want to print out a product of mulitple variables with indices such as , which in Latex would be $A_{ 0042 }*A_{ 3141 }*A_{ 2718 }*A_{ 0042 }$ The following code does the job with named fields so that for many indices it stays readable:

idx_mapping = {'i1':42, 'i2':3141, 'i3':2178 }
print('$A_{{ {i1:04d} }} * A_{{ {i2:d} }} * A_{{ {i3:d} }} * A_{{ {i1:04d} }}$'.format(**idx_mapping))

回答12:

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}')

来源：https://stackoverflow.com/questions/5466451/how-can-i-print-literal-curly-brace-characters-in-python-string-and-also-use-fo