How to Match Multiline Text Blocks with Python Regular Expressions: Capturing Lowercase and Uppercase Components?

Matching Multiline Text Blocks with Python Regular Expressions

In this programming question, we aim to match a specific format of text that spans multiple lines. The input text consists of alternating blocks of lowercase and uppercase text, where the lowercase text represents a base component, and the uppercase text represents a sequence of amino acids.

Problem Statement

The task is to create a regular expression in Python that can capture two components from the input text:

1. The base lowercase component
2. The sequence of uppercase lines that appears two lines below it

The output should be divided into two capture groups, with the base lowercase component in group(1) and the uppercase sequence in group(2).

Solution

To solve this problem, we can utilize the following regular expression:

re.compile(r"^(.+)\n((?:\n.+)+)", re.MULTILINE)

This regex operates in multiline mode, meaning that the ^ and $ anchors will match the beginning and end of lines, respectively.

Explanation

• ^(. )$: Matches the base lowercase component on its own line.

• n((?:n. ) ): Matches consecutive lines of uppercase text that follow the base component.

  • n: Matches a linefeed character.
  • (?:n. ) : A non-capturing group that matches one or more occurrences of a linefeed followed by one or more non-whitespace characters ( ).

Usage

To use this regex, you can follow these steps:

import re

text = """
some Varying TEXT
...
[lines of uppercase text]
...
"""

regex = re.compile(r"^(.+)\n((?:\n.+)+)", re.MULTILINE)

match = regex.search(text)
if match:
    lowercase_text = match.group(1)
    uppercase_text = match.group(2)
    # Process the captured text as needed

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