Flatten example in python to flatten nested array

flatten.py

#[[1,2,[3]],4] -> [1,2,3,4]
import ast

def flatten(nested_array, flat_array):

	for entry in nested_array:
		if type(entry) is list: 
			flatten(entry, flat_array)
		else:
			flat_array.append(entry)
	return flat_array;

def get_input():

	nested_input = ast.literal_eval(raw_input("Enter a nested array : "));
	if type(nested_input) is list:
		return nested_input
	else:
		print('invalid input\n')
		get_input();

print(flatten(get_input(), []))