len

len(s)

Returns the length of an object (built-in).

s	a sequence (string, bytes, tuple, list, or range) or a collection (dictionary, set or frozen set)

REMARKS

* This is a built-in function.
* Return the length (the number of items) of an object. The argument may be a sequence (such as a string, bytes, tuple, list, or range) or a collection (such as a dictionary, set, or frozen set).
* For the Official documentation refer to python.org

testList = [] 
print(testList, 'length is', len(testList))               #= [] length is 0 

testList = [1, 2, 3] 
print(testList, 'length is', len(testList))               #= [1, 2, 3] length is 3 

testTuple = (1, 2, 3) 
print(testTuple, 'length is', len(testTuple))             #= (1, 2, 3) length is 3 

testRange = range(1, 10) 
print('Length of', testRange, 'is', len(testRange))       #= Length of range(1, 10) is 9