def satisfiesF(L):
    """
    Assumes L is a list of strings
    Assume function f is already defined for you and it maps a string to a Boolean
    Mutates L such that it contains all of the strings, s, originally in L such
            that f(s) returns True, and no other elements
    Returns the length of L after mutation
    """
    for e in L:
        if not f(e):
            alis.remove(e)
    print len(L)
    print L
def f(x):
	return 'a' in x
 
satisfiesF(['ava','nlki','qorqorj','jaja'])
satisfiesF([])
satisfiesF(['','fafs'])
 

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