Difference between `findall()` and `finditer()` in Python’s `re` module

[Splendid Digital Solutions]

Difference between finditer and findall as part of re module
byu/DigitalSplendid inlearnpython

Source: Created with AI tool

Let’s break this down step by step and explain the difference between finditer() and findall() in Python’s re module.

Code Overview

This function re_pattern(text, pattern) does two things:
1. It prints the full text string.
2. It uses re.finditer() to find all occurrences of the regular expression pattern in the text and then prints detailed information about each match.

Explanation: Step by Step

def re_pattern(text, pattern):
print(" '{}'".format(text))

for match in re.finditer(pattern, text):
s = match.start()
e = match.end()
substr_match = text[s:e]
dot_prefix = '.' * s
print(" {}'{}'".format(dot_prefix, substr_match))

1. print(" '{}'".format(text)): This prints the full input string. The format() method is used to insert the text variable into the output string.

2. for match in re.finditer(pattern, text)::

– This is where the core of the operation happens. It uses the re.finditer() function to find all matches of the regular expression pattern in the text.
– re.finditer() returns an iterator that yields match objects one by one. Each match object contains detailed information about each match, including the substring that was matched and the position (start and end indexes) in the text where the match was found.

finditer() vs. findall() Explained

Both finditer() and findall() are used to search for patterns in text, but they differ in how they return the results:

• findall():
• What it returns: A list of all matched substrings. It simply extracts all the matches and returns them in a list.
• Memory Usage: Since findall() returns a list, it holds all matches in memory at once. This can be inefficient if there are many matches or if the text is large, as it requires storing the entire list in RAM.

Example:

matches = re.findall(r'\d+', 'There are 3 apples and 4 bananas.')
print(matches) # Output: ['3', '4']

• finditer():
• What it returns: An iterator of match objects. It doesn’t return the matches directly but yields match objects as they are found. You can then retrieve detailed information about each match from these match objects (such as the matched string, start and end positions, etc.).
• Memory Usage: Since finditer() returns an iterator, it doesn’t load all the matches into memory at once. Instead, it yields them one by one as you iterate over the results, making it more memory-efficient for large texts or large numbers of matches. The match objects do take up some memory, but they are generally more lightweight compared to storing all the matched strings in a list.

Example:

matches = re.finditer(r'\d+', 'There are 3 apples and 4 bananas.')
for match in matches:
print(match.group()) # Output: '3' and '4'

Memory and Computational Resource Considerations

• Computational Resource Usage:
• finditer() does take slightly more computational resources compared to findall(), as it has to create a match object for each match. This object includes extra details like the start and end positions of the match.
• However, this extra computation only happens once for each match, and after yielding the match, no further computation is necessary. The iterator itself doesn’t require storing all the matches in memory, which makes it more memory efficient than findall() for large datasets.

[Author]

Posts