Python：如何替换由某些字符括起来的字符串

Question

I want to replace a certain variable name in a mathematical expression while avoid to replace in function names.

For example following replacement of n :

sin(2 pi*nd)" -> "sin(2 pi*REPL d) but not: siREPL(2 pi*REPL d)

My idea was to check whether the substr is enclosed by special characters ( ' ' , '(' , '*' , etc) at one side but I failed to put it in regex or python code.

Any ideas?

Answer 1

Use word boundary( \\b )

>>> import re
>>> re.sub(r'\bn\b', 'REPL', 'sin(2 pi*n d)')
'sin(2 pi*REPL d)'

According to the re module documentation :

\\b

Matches the empty string, but only at the beginning or end of a word. A word is defined as a sequence of alphanumeric or underscore characters, so the end of a word is indicated by whitespace or a non-alphanumeric, non-underscore character. Note that formally, \\b is defined as the boundary between a \\w and a \\W character (or vice versa), or between \\w and the beginning/end of the string, ...