python - How can I print literal curly-brace characters in a 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

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 2

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}

Answer 3

You escape it by doubling the braces.

Eg:

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

Answer 4

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.

Answer 5

Try doing this:

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

Answer 6

Try this:

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

Answer 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

Answer 8

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}}'

Answer 9

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).

Answer 10

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.

Answer 11

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)  

Answer 12

I am ridiculously late to this party. I am having success placing the brackets in the replacement element, like this:

print('{0} {1}'.format('{hello}', '{world}'))

which prints

{hello} {world}

Strictly speaking this is not what OP is asking, as s/he wants the braces in the format string, but this may help someone.

Answer 13

You can use a "quote wall" to separate the formatted string part from the regular string part.

From:

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

to

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

---

A clearer example would be

string = 10
print(f"{string} {word}")

Output:

NameError: name 'word' is not defined

Now, add the quote wall like so:

string = 10
print(f"{string}"" {word}")

Output:

10 {word}

Answer 14

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('$A_{{ {i1:04d} }} * A_{{ {i2:04d} }} * A_{{ {i3:04d} }} * A_{{ {i1:04d} }}$'.format(**idx_mapping))

Answer 15

I used a double {{ }} to prevent fstring value injection,

for example, heres my Postgres UPDATE statement to update a integer array column that takes expression of {} to capture the array, ie:

ports = '{100,200,300}'

with fstrings its,

ports = [1,2,3]

query = f"""
   UPDATE table SET ports = '{{{ports}}}' WHERE id = 1
"""

the actual query statement will be,

UPDATE table SET ports = '{1,2,3}'

which is a valid postgres satement

Answer 16

f-strings (python 3)

You can avoid having to double the curly brackets by using f-strings only for the parts of the string where you want the f-magic to apply, and using regular strings for everything that is literal. Let python do the string joining for you simply by stacking stacking multiple strings together.

number = 42
print(" { Hello }"  
f" {number} " 
"{ thanks for all the fish }")

### OUTPUT:
{ Hello } 42 { thanks for all the fish }

NOTE: There is no need for line breaks. I have only put them in order to make it more readable. You could as well write it as "{Hello}"f"{number}".

Answer 17

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 18

If you need curly braces within a f-string template that can be formatted, you need to output a string containing two curly braces within a set of curly braces for the f-string:

css_template = f"{{tag}} {'{{'} margin: 0; padding: 0;{'}}'}"
for_p = css_template.format(tag="p")
# 'p { margin: 0; padding: 0;}'

Answer 19

Or just parametrize the bracket itself? Probably very verbose.

x = '{open_bracket}42{close_bracket}'.format(open_bracket='{', close_bracket='}') 
print(x)
# {42}

Answer 20

When you're just trying to interpolate code strings I'd suggest using jinja2 which is a full-featured template engine for Python, ie:

from jinja2 import Template

foo = Template('''
#include <stdio.h>

void main() {
    printf("hello universe number {{number}}");
}
''')

for i in range(2):
    print(foo.render(number=i))

So you won't be enforced to duplicate curly braces as the whole bunch of other answers suggest

Answer 21

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 22

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