How to implement a verbose REGEX in Python

Question

I am trying to use a verbose regular expression in Python (2.7). If it matters I am just trying to make it easier to go back and more clearly understand the expression some

Answer 1

• It is a good habit to use raw string literals when defining regex patterns. A lot of regex patterns use backslashes, and using a raw string literal will allow you to write single backslashes instead of having to worry about whether or not Python will interpret your backslash to have a different meaning (and having to use two backslashes in those cases).

• \b? is not valid regex. This is saying 0-or-1 word boundaries. But either you have a word boundary or you don't. If you have a word boundary, then you have 1 word boundary. If you don't have a word boundary then you have 0 word boundaries. So \b? would (if it were valid regex) be always true.

• Regex makes a distinction between the end of a string and the end of a line. (A string may consist of multiple lines.)

  • \A matches only the start of a string.
  • \Z matches only the end of a string.
  • $ matches the end of a string, and also end of a line in re.MULTILINE mode.
  • ^ matches the start of a string, and also start of a line in re.MULTILINE mode.

---

import re
verbose_item_pattern = re.compile(r"""
    $            # end of line boundary
    \s{1,2}      # 1-or-2 whitespace character, including the newline
    I            # a capital I
    [tT][eE][mM] # one character from each of the three sets this allows for unknown case
    \s+          # 1-or-more whitespaces INCLUDING newline
    \d{1,2}      # 1-or-2 digits
    [.]?         # 0-or-1 literal .
    \(?          # 0-or-1 literal open paren
    [a-e]?       # 0-or-1 letter in the range a-e
    \)?          # 0-or-1 closing paren
    .*           # any number of unknown characters so we can have words and punctuation
    [^0-9]       # anything but [0-9]
    $            # end of line boundary
    """, re.VERBOSE|re.MULTILINE)

x = verbose_item_pattern.search("""
 Item 1.0(a) foo bar
""")

print(x)

yields

<_sre.SRE_Match object at 0xb76dd020>

(indicating there is a match)

Answer 2

As say in the comment you should escape your backslash or use raw string even with triple quote.

verbose_item_pattern = re.compile(r"""
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