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f-string cannot contain backslash characters
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Fixed in Python 3.12
f-string backslashSyntaxErrorstring formattingescape sequence
Error Messages
SyntaxError: f-string expression part cannot include a backslashProblem
Using backslashes inside f-string expressions raises SyntaxError. For example: f'{"\n".join(items)}' fails. This is a common gotcha when trying to use escape sequences or regex in f-strings.
Solution
Assign the expression with backslash to a variable first:
# BAD
result = f'{"\n".join(items)}' # SyntaxError
# GOOD
newline = '\n'
result = f'{newline.join(items)}'
# Or use chr()
result = f'{chr(10).join(items)}'
# Or don't use f-string for this
result = '\n'.join(items)
# Python 3.12+ lifts this restriction!
# BAD
result = f'{"\n".join(items)}' # SyntaxError
# GOOD
newline = '\n'
result = f'{newline.join(items)}'
# Or use chr()
result = f'{chr(10).join(items)}'
# Or don't use f-string for this
result = '\n'.join(items)
# Python 3.12+ lifts this restriction!
Why
Python's parser cannot handle backslash escapes inside the curly braces of f-strings in versions before 3.12. The f-string parser and the string escape parser conflict.
Gotchas
- Python 3.12 removes this restriction — backslashes work in f-string expressions
- This also affects raw strings and regex patterns inside f-strings
- chr(10) for newline and chr(9) for tab are workarounds
Code Snippets
Backslash workaround in f-strings
items = ['a', 'b', 'c']
# SyntaxError in Python < 3.12
# result = f'{chr(92).join(items)}'
# Workaround
sep = '\n'
result = f'{sep.join(items)}'Context
When using escape characters inside f-string expressions
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