Four Python Tricks to Count the Number of 1s in a List

The author, a Python enthusiast, answers a fan's question about counting the occurrences of the number 1 in a list.

Implementation ideas

Several approaches are possible, such as using len(), list comprehensions, Counter, and the list count() method.

Methods

Method 1

Using an anonymous function (lambda) together with filter:

a = [1,0,2,0,1]
b = list(filter(lambda x: x == 1, a))
print(b)
print(f"1的个数：{len(b)}")

Method 2

Using a list comprehension:

a = [1, 0, 2, 0, 1]
b = [x for x in a if x == 1]
print(len(b))
print(f"1的个数：{len(b)}")

Method 3

Using collections.Counter to obtain a dictionary of element frequencies:

from collections import Counter
a = [1, 0, 2, 0, 1]
b = Counter(a)
print(b)

Method 4

Using the list count method directly:

a = [1, 0, 2, 0, 1]
print(a.count(1))
print(f"1的个数：{a.count(1)}")

Conclusion

The article presents four concise Python solutions for counting the number of 1s in a list, illustrating the use of lambda + filter, list comprehension, Counter, and the built‑in count() method.