Python code to check if an array has a sequence (1,3,4)

I recently applied for a job as a Python coder but was rejected.

This was the problem:


Write a python code to check if an array has a sequence (1,3,4)

Assuming they were looking for expert Python programmers, what could I have done better?

# Tested with Python 2.7
import unittest

# Runtime: O(n)

def doesSeqAppear(int_arr):
    #check if input is a list
    if not isinstance(int_arr, list):
        raise TypeError("Input shall be of type array.")

    # check all elements are of type int
    if not all(isinstance(item, int) for item in int_arr) :
        raise ValueError("All elements in array shall be of type int.")

    arr_len = len(int_arr)
    if arr_len < 3: 
        return False

    # Loop through elements
    for i in range(arr_len-2):
        if int_arr[i] == 1 and \
            int_arr[i+1] == 3 and \
            int_arr[i+2] == 4 : 
            return True
    return False

class TestMethodDoesSeqAppear(unittest.TestCase):
    def test_only_single_seq(self):
        #Single time
        assert doesSeqAppear([1,3,4]) == True

    def test_multiple_seq(self):
        #multiple
        assert doesSeqAppear([2,2,1,3,4,2,1,3,4]) == True

    def test_neg_seq(self):
        #multiple
        assert doesSeqAppear([9,-1,1,3,4,-4,4]) == True

    def test_only_empty_seq(self):
        #empty
        assert doesSeqAppear([]) == False
    def test_only_single_elem_seq(self):
        #Single element
        assert doesSeqAppear([1]) == False

    def test_input_is_none(self):
        self.assertRaises(TypeError, doesSeqAppear, None)

    def test_raises_type_error(self):
        self.assertRaises(TypeError, doesSeqAppear, "string")

    def test_raises_value_error(self):
        self.assertRaises(ValueError, doesSeqAppear, [1,2,'a', 'b'])

if __name__ == '__main__':
    unittest.main()

#

By PEP 8, doesSeqAppear should be does_seq_appear. You used the right naming convention for your unit tests, though. Personally, I would prefer def contains_seq(arr, seq=[1, 3, 4]).

Your arr_len < 3 test is superfluous and should therefore be eliminated. Don't write a special case when the regular case works correctly and just as quickly.

Your all(isinstance(item, int) for item in int_arr) check was not specified in the problem, and is therefore harmful. The question does not say that doesSeqAppear([3.1, 1, 3, 4]) should return False, nor does it say that it should fail with an exception. In fact, by my interpretation, it does contain the magic sequence and should therefore return True. In any case, you have wasted a complete iteration of the list just to perform a check that wasn't asked for.

Checking isinstance(int_arr, list) is un-Pythonic, since duck-typing is the norm in Python. In any case, the code would likely fail naturally if it is not a list.

After cutting all that excess, you should drop the # Loop through elements comment as well.

StackExchange Code Review Q#149867, answer score: 10