How do you use backslash in python f

In Python >=3.6, f-strings can be used as a replacement for the str.format method. As a simple example, these are equivalent:

'{} {}'.format(2+2, "hey")
f'{2+2} {"hey"}'

Disregarding format specifiers, I can basically move the positional arguments of str.format inside braces in an f-string. Note specifically that I am allowed to just put str literals in here, although it may seem a bit unwieldy.

There are however some limitations. Specifically, backslashes in any shape or form are disallowed inside the braces of an f-string:

'{}'.format("new\nline")  # legal
f'{"new\nline"}'          # illegal
f'{"\\"}'                 # illegal

I cannot even use \ to split up a long line if it's inside the braces;

f'{2+\
2}'     # illegal

even though this usage of \ is perfectly allowed inside normal str's;

'{\
}'.format(2+2)  # legal

It seems to me that a hard stop is coded into the parser if it sees the \ character at all inside the braces of an f-string. Why is this limitation implemented? Though the docs specify this behavior, it does not justify why.

SyntaxError: f-string expression part cannot include a backslash #

The Python "SyntaxError: f-string expression part cannot include a backslash" occurs when we use a backslash between the curly braces of a formatted string. To solve the error, store the backslash character in a variable or move it out of the curly braces of the f-string.

Here is an example of how the error occurs.

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first = 'James'
last = 'Doe'

# ⛔️ SyntaxError: f-string expression part cannot include a backslash
result = f'{first\n}{last}'

We can't use a backslash in the expression part (the curly braces) of a formatted string literal.

One way to solve the error is to extract the \ or the \n character in a variable.

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first = 'James'
last = 'Doe'

nl_char = '\n' * 2

result = f'{first}{nl_char}{last}'

# James

# Doe
print(result)

A backslash character cannot be directly in the expression part of an f-string, but we can extract it in a variable and interpolate the variable in the string.

If your use case doesn't require an expression, and all you have is a backslash or a \n char, move it out of the curly braces.

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first = 'James'
last = 'Doe'

result = f'{first}\n{last}'

# James
# Doe
print(result)

Here is another example of extracting a newline char in a variable, so we can use it in the expression of an f-string.

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employees = ['Alice', 'Bob', 'Carl']

newline_char = '\n'

my_str = f'Employees list: \n{newline_char.join(employees)}'

# Employees list:
# Alice
# Bob
# Carl
print(my_str)

Formatted string literals (f-strings) let us include expressions inside of a string by prefixing the string with f.

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my_str = 'is subscribed:'

my_bool = True

result = f'{my_str} {my_bool}'

print(result)  # 👉️ is subscribed: True

Make sure to wrap expressions in curly braces - {expression}.

Conclusion #

The Python "SyntaxError: f-string expression part cannot include a backslash" occurs when we use a backslash between the curly braces of a formatted string. To solve the error, store the backslash character in a variable or move it out of the curly braces of the f-string.

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Can you use \n in F strings?