How Can I Use Variables in Python Regular Expressions for Dynamic Pattern Matching?

Incorporating Variables into Regular Expressions in Python

While regular expressions are incredibly useful for finding patterns in text, it can sometimes be advantageous to incorporate dynamic values into the search criteria. In Python, this can be achieved by constructing the regular expression as a string.

Consider the following scenario where you want to search for a specific word within a text, but the word itself is stored in a variable called TEXTO:

TEXTO = sys.argv[1]

To include this variable in your regular expression, you can concatenate it with the desired pattern as follows:

my_regex = r"\b(?=\w)" + re.escape(TEXTO) + r"\b(?!\w)"

Here's a breakdown of the components:

• b: Matches a word boundary.
• (?=w): Positive lookahead assertion, ensuring that there is a word character after the text.
• re.escape(TEXTO): Escapes special characters within TEXTO to prevent their interpretation as metacharacters.
• b(?!w): Negative lookahead assertion, ensuring that there is no word character before the text.

With the fully constructed regular expression, you can proceed with your match attempt:

if re.search(my_regex, subject, re.IGNORECASE):
    # Successful match
else:
    # Match attempt failed

Note that the use of re.escape() is crucial if TEXTO contains any special characters, such as . or , which could interfere with the pattern matching. By escaping these characters, they are treated as literal characters rather than metacharacters.

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