To count the occurrences of a particular substring in a list of strings in Python, we can use several methods. In this article, we are going to explore different methods to count the existence of a particular substring in a given list.

Using sum() and Generator Expression

This method uses a generator expression inside the sum() function. It's similar to list comprehension but a bit more memory efficient since it doesn't create a new list.

x = ["hello", "world", "hi", "hello world"]

# Use a generator expression to iterate through 
# the list and count matches
# For each string (y) in the list (x), check if "hello" is present
count = sum(1 for y in x if "hello" in y)
print(count)

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• The generator expression (1 for y in x if "hello" in y) generates a 1 for each string in x that contains "hello". Then sum() adds them up to give the total count.

There are multiple other ways to count strings containing a substring in Python.

Using List Comprehension

If we have to make the code shorter and cleaner we can use list comprehension. This method lets us create a list of all strings that contain the substring and then just count how many there are.

x = ["hello", "world", "hi", "hello world"]

# Count the number of strings in the new list using len()
count = len([y for y in x if "hello" in y])
print(count)

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Using filter() Function

filter() function allows us to filter the list based on a condition. We can filter out the strings that don’t contain the substring and then count the remaining ones.

x = ["hello", "world", "hi", "hello world"]

# Use the filter() function to filter out strings containing "hello"
count = len(list(filter(lambda y: "hello" in y, x)))
print(count)

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• filter() goes through each string in x and applies the condition lambda y: "hello" in y. It keeps only the strings where "hello" is found.
• We then count the length of the filtered list using len().

Using for loop

Using a for loop is the easiest way to count strings with a substring. We can go through each string in the list and check if the substring is present.

x = ["hello", "world", "hi", "hello world"]

count = 0
# Iterate through each string (y) in the list (x)
for y in x:
    if "hello" in y:
        count += 1
print(count)

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