Delving Deeper

Embedding Flags and Patterns

In situations where flags cannot be added when compiling an expression, such as when a pattern is passed as an argument to a library function that will compile it later, the flags can be embedded inside the expression string itself. For example, to turn case-insensitive matching on, add (?i) to the beginning of the expression.

# re_flags_embedded.py

import re

text = 'This is some text -- with punctuation.'
pattern = r'(?i)\bT\w+'
regex = re.compile(pattern)

print('Text      :', text)
print('Pattern   :', pattern)
print('Matches   :', regex.findall(text))

Because the options control the way the entire expression is evaluated or parsed, they should always appear at the beginning of the expression.

$ python3 re_flags_embedded.py

Text      : This is some text -- with punctuation.
Pattern   : (?i)\bT\w+
Matches   : ['This', 'text']

The abbreviations for all of the flags are listed in the table below.

Embedded flags can be combined by placing them within the same group. For example, (?im) turns on case-insensitive matching for multiline strings.