How to extract a number from an alphanumeric string in Python?

Question

I want to extract numbers contained in an alphanumeric strings. Please help me on this.

Example:

line = ["frame_117", "frame_11","frame_1207"]

Result:

[117, 11, 1207]

Answer 1

import re
temp = []
lines = ["frame_117", "frame_11","frame_1207"]
for line in lines:
    num = re.search(r'-?\d+', line)
    temp.append(int(num.group(0)))

print(temp) # [117, 11, 1207]

Answer 2

You can split with special character '_' like this:

numbers = []
line = ["frame_117", "frame_11","frame_1207"]
for item in line:
    number = int(item.split("_",1)[1])
    numbers.append(number)
print(numbers)

Answer 3

Rationale

The first thing I see is that the names inside the list have a pattern. The string frame, an underscore _ and the string number: "frame_number".

Step-By-Step

With that in mind, you can:

1. Loop through the list. We'll use a list comprehension.
2. Get each item from the list (the names="frame_number" )
3. Split them according to a separator (getting a sublist with ["frame", "number"])
4. And then create a new list with the last items of each sublist

numbers = [x.split("_")[-1] for x in line]
['117', '11', '1207']

Solution

5. But you need numbers and here you have a list of strings. We make one extra step and use int().

numbers = [int(x.split("_")[-1]) for x in line]
[117, 11, 1207]

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This works only because we detected a pattern in the target name.

But what happens if you need to find all numbers in a random string? Or floats? Or Complex numbers? Or negative numbers?

That's a little bit more complex and out of scope of this answer. See How to extract numbers from a string in Python?