In python with explanation please.

4. Write a function extractInt() that takes a string as a parameter and returns an integer constructed out of the digits that appear in the string. The digits in the integer should appear in the same order as the digits in the string. If the string does not contain any digits or an empty string is provided as a parameter, the value O should be return. The following shows several sample executions of the function: Python 3.6.2 Shell - O X File Edit Shell Debug Options Window Help >>> extract Int ('1, 2, 3 ... we have been counting') 123 >>> val = extractInt(' Testing 1. Testing 12. Testing again!!") >>> val 112 >>> val * 2 224 >>> extract Int ("1 2 3 o'clock, 5 6 7 o'clock, 8 9 10 o'clock") 1235678910 >>> extractInt('no digits -- hou sad!") >>> extractInt('"') >>> | Ln: 69 Col: 4