💬 Question: Which method finds the list of all occurrences of the pattern in the given string?
Problem Formulation: Given a longer string and a shorter string. How to find all occurrences of the shorter string in the longer one?
Consider the following example:
- Longer string:
'Finxters learn Python with Finxter'
- Shorter string pattern:
- Result 1:
Optionally, you may also want to get the positions where the shorter string arise in the longer string:
- Result 2:
[(0, 'Finxter'), (27, 'Finxter')]
Method 1: Regex re.finditer()
To get all occurrences of a pattern in a given string, you can use the regular expression method
re.finditer(pattern, string). The result is an iterable of match objects—you can retrieve the indices of the match using the
import re s = 'Finxters learn Python with Finxter' pattern = 'Finxter' # Method 1: re.finditer for m in re.finditer(pattern, s): print(pattern, 'matched from position', m.start(), 'to', m.end())
The output is:
Finxter matched from position 0 to 7 Finxter matched from position 27 to 34
🌍 Related Tutorial: Python Regex Finditer
Method 2: re.finditer() + List Comprehension
To get the pattern string, start index, and end index of the match into a list of tuples, you can use the following one-liner based on list comprehension:
[(pattern, m.start(), m.end()) for m in re.finditer(pattern, s)].
import re s = 'Finxters learn Python with Finxter' pattern = 'Finxter' # Method 2: re.finditer + list comprehension l = [(pattern, m.start(), m.end()) for m in re.finditer(pattern, s)] print(l)
The output is:
[('Finxter', 0, 7), ('Finxter', 27, 34)]
🌍 Related Tutorial: Python List Comprehension
Method 3: Python String startswith()
startswith(prefix, start) method checks whether a given string starts with a prefix when starting to search for the
prefix at the index
We can use the
startswith() method in a list comprehension statement to find all occurrences (positions) of a substring in a given string like so:
[i for i in range(len(s)) if s.startswith(pattern, i)]
Here’s the full example using this approach:
s = 'Finxters learn Python with Finxter' pattern = 'Finxter' # Method 4: startswith() to find all occurrences of substring in string l = [i for i in range(len(s)) if s.startswith(pattern, i)] print(l)
The output shows a list of start indices where the substring (pattern) was found in the original string:
It pays to learn the basics in Python—feel free to dive deeper into this method in the following Finxter blog tutorial only one click away:
🌍 Related Tutorial: Python String Startswith
Method 4: re.findall()
If you’re interested in only the matched substrings without their index location in the given string, you can use the following approach.
To find all substrings in a given string, use the
re.findall(substring, string) function that returns a list of matching substrings—one per match.
import re s = 'Finxters learn Python with Finxter' pattern = 'Finxter' # Method 4: re.findall() to find all patterns in string l = re.findall(pattern, s) print(l) # ['Finxter', 'Finxter']
In case you wonder how the
regex.findall() method works, have a look at this graphic:
🌍 Related Tutorial: Python Regex Findall
Method 5: No-Regex, Recursive, Overlapping
The following method is based on recursion and it doesn’t require any external library.
The idea is to repeatedly find the next occurrence of the substring pattern in the string and call the same method recursively on a shorter string—moving the start position to the right until no match is found anymore.
All found substring matches are accumulated in a variable
acc as you go through the recursion calls.
s = 'Finxters learn Python with Finxter' pattern = 'Finxter' # Method 5: recursive, without regex def find_all(pattern, # string pattern string, # string to be searched start=0, # ignore everything before start acc=): # All occurrences of string pattern in string # Find next occurrence of pattern in string i = string.find(pattern, start) if i == -1: # Pattern not found in remaining string return acc return find_all(pattern, string, start = i+1, acc = acc + [(pattern, i)]) # Pass new list with found pattern l = find_all(pattern, s) print(l)
The output is:
[('Finxter', 0), ('Finxter', 27)]
Note that this method also finds overlapping matches—in contrast to the regex methods that consume all partially matched substrings.
Where to Go From Here?
Enough theory. Let’s get some practice!
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While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
To help students reach higher levels of Python success, he founded the programming education website Finxter.com that has taught exponential skills to millions of coders worldwide. He’s the author of the best-selling programming books Python One-Liners (NoStarch 2020), The Art of Clean Code (NoStarch 2022), and The Book of Dash (NoStarch 2022). Chris also coauthored the Coffee Break Python series of self-published books. He’s a computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.