>>> from phone import prefix

>>> v1 = ['934780245', '012', '618776611', '972399700', '11811',
...    '972399700', '012', '938765454', '012', '11811', '012', '11811']
>>> with open ('calls.txt', 'w') as f:
...    for e in v1:
...        a = f.write (e + '\n')
>>> prefix('calls.txt', 'result1.txt', '93')
>>> with open ('result1.txt', 'r') as f:
...    a1 = f.read()
>>> a1
'934780245\n938765454\n'

>>> prefix('calls.txt', 'result2.txt', '972')
>>> with open ('result2.txt', 'r') as f:
...    a2 = f.read()
>>> a2
'972399700\n972399700\n'