Question: 
Write a function to count character frequency of a given string.


Model's Code:
def char_frequency(s):
    frequency = {}
    for char in s:
        frequency[char] = frequency.get(char, 0) + 1
    return frequency



Sample Correct Code:
def char_frequency(str1):
    dict = {}
    for n in str1:
        keys = dict.keys()
        if n in keys:
            dict[n] += 1
        else:
            dict[n] = 1
    return dict


Asserts:
assert char_frequency('python')=={'p': 1, 'y': 1, 't': 1, 'h': 1, 'o': 1, 'n': 1}
assert char_frequency('program')=={'p': 1, 'r': 2, 'o': 1, 'g': 1, 'a': 1, 'm': 1}
assert char_frequency('language')=={'l': 1, 'a': 2, 'n': 1, 'g': 2, 'u': 1, 'e': 1}


Tests:
Test 1 of 3: PASS
Test 2 of 3: PASS
Test 3 of 3: PASS

Test 332 of 974: 239/332 (71.98795180722891%): success