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Table of Contents
What are combinations ?
Example 1: Select a combination of 2 elements from the list
Example 2: Take a combination of 3 characters in a string
Example 3: Find the combination of the sum of two numbers in the numeric list equals the target value
Tips: Combination vs Arrangement
Practical application scenarios
Home Backend Development Python Tutorial python itertools combinations example

python itertools combinations example

Jul 31, 2025 am 09:53 AM
java programming

Itertools.combinations is used to generate all non-repetitive combinations (order irrelevant) that selects a specified number of elements from the iterable object. Its usage includes: 1. Select 2 element combinations from the list, such as ('A', 'B'), ('A', 'C'), etc., to avoid duplicate order; 2. Take 3 character combinations of strings, such as "abc" and "abd", which are suitable for subsequence generation; 3. Find the combinations whose sum of two numbers is equal to the target value, such as 1 5=6, simplify the double loop logic; the difference between combinations and arrangement lies in whether the order is important. Combinations regard AB and BA as the same, while permutations are regarded as different; this tool is suitable for course selection, team formation, game competition, feature combination and algorithm enumeration, and the code is concise and efficient, suitable for dealing with the problem of "selecting but not ranking".

python itertools combinations example

itertools.combinations is a very practical tool in Python to generate all non-repetitive combinations (independent order) that select a specified number of elements from a given iterable object. The following are some common examples to illustrate its usage.

python itertools combinations example

What are combinations ?

itertools.combinations(iterable, r)

  • iterable : input data, such as lists, strings, etc.
  • r : The number of elements selected each time
  • Returns an iterator containing all combinations of length r , non-repeat and out of order

Example 1: Select a combination of 2 elements from the list

 import itertools

items = ['A', 'B', 'C', 'D']
comb = itertools.combinations(items, 2)

for c in comb:
    print(c)

Output:

python itertools combinations example
 ('A', 'B')
('A', 'C')
('A', 'D')
('B', 'C')
('B', 'D')
('C', 'D')

Note: ('A', 'B') and ('B', 'A') are considered the same combination, so they only appear once.


Example 2: Take a combination of 3 characters in a string

 import itertools

s = "abcd"
comb = itertools.combinations(s, 3)

for c in comb:
    print(''.join(c))

Output:

python itertools combinations example
 abc
abd
acd
bcd

This is useful in generating codons, subsequences and other scenarios.


Example 3: Find the combination of the sum of two numbers in the numeric list equals the target value

 import itertools

numbers = [1, 2, 3, 4, 5]
target = 6

comb = itertools.combinations(numbers, 2)
for a, b in comb:
    if ab == target:
        print(f"{a}  = {target}")

Output:

 1 5 = 6
2 4 = 6

Avoid manual writing double loops, making the code clearer.


Tips: Combination vs Arrangement

  • combinations : order is irrelevant, AB and BA are one
  • permutations : The order is related, AB and BA are two types
 list(itertools.combinations('AB', 2)) # [('A', 'B')]
list(itertools.permutations('AB', 2)) # [('A', 'B'), ('B', 'A')]

Practical application scenarios

  • Select a combination of several items from multiple options (such as: selecting courses, forming teams)
  • Enumerate all possible pairings (such as match vs.)
  • Attempts to combine features in data analysis
  • Violent enumeration solution space in algorithm problems

Basically that's it. itertools.combinations is simple to use, but it is especially suitable for dealing with the problem of "selecting but not ranking". It is much cleaner to write than nested for loops.

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