Varying Arguments¶

In Python we can pass different number of arguments of same type while invoking functions. Let’s talk about Varying arguments.

At times we might want to pass values of same type as arguments and we might not know how many of them.
In that scenario we can leverage the concept of Varying arguments.
The parameter which accepts Varying arguments should have * at the beginning - example: *phone_numbers.
As part of the function body the type of the parameter will be tuple. In our case, as we will be passing phone numbers as strings, it will be of type tuple where each element will be of type string.

def get_invalid_phone_count(*phone_numbers, employee_id):
    invalid_count = 0
    for phone_number in phone_numbers:
        if len(phone_number) < 10:
            invalid_count += 1
    return employee_id, invalid_count

s = 'Employee {employee_id} have {invalid_count} invalid phones'
employee_id, invalid_count = get_invalid_phone_count('1234', '1234567890', 1) 
# argument by position will fail
# Python interpreter cannot determine whether 1 is related to phone_numbers or employee_id

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-0fa187d3d10e> in <module>
      1 s = 'Employee {employee_id} have {invalid_count} invalid phones'
----> 2 employee_id, invalid_count = get_invalid_phone_count('1234', '1234567890', 1)
      3 # argument by position will fail
      4 # Python interpreter cannot determine whether 1 is related to phone_numbers or employee_id

TypeError: get_invalid_phone_count() missing 1 required keyword-only argument: 'employee_id'

s = 'Employee {employee_id} have {invalid_count} invalid phones'
phone_numbers = ('1234', '1234567890',)
employee_id, invalid_count = get_invalid_phone_count(employee_id=1, phone_numbers=phone_numbers) 
# argument by name will fail
# This will fail as we cannot pass varrying argument using keyword

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-05a120172b4e> in <module>
      1 s = 'Employee {employee_id} have {invalid_count} invalid phones'
      2 phone_numbers = ('1234', '1234567890',)
----> 3 employee_id, invalid_count = get_invalid_phone_count(employee_id=1, phone_numbers=phone_numbers)
      4 # argument by name will fail
      5 # This will fail as we cannot pass varrying argument using keyword

TypeError: get_invalid_phone_count() got an unexpected keyword argument 'phone_numbers'

s = 'Employee {employee_id} have {invalid_count} invalid phones'
employee_id, invalid_count = get_invalid_phone_count('1234', '1234567890', employee_id=1) 
# argument by position will fail
# Python interpreter cannot determine whether 1 is related to phone_numbers or employee_id

print(s.format(employee_id=employee_id, invalid_count=invalid_count))

Employee 1 have 1 invalid phones

def get_invalid_phone_count(employee_id, *phone_numbers):
    print(f'Length of phone_numbers is: {len(phone_numbers)}')
    print(f'Type of phone_numbers is: {type(phone_numbers)}')
    print(f'Type of each phone number is: {type(phone_numbers[0])}')
    print(phone_numbers)
    invalid_count = 0
    for phone_number in phone_numbers:
        if len(phone_number) < 10:
            invalid_count += 1
    return employee_id, invalid_count

s = 'Employee {employee_id} have {invalid_count} invalid phones'
employee_id, invalid_count = get_invalid_phone_count(1, '1234', '1234567890') # argument by position works here

Length of phone_numbers is: 2
Type of phone_numbers is: <class 'tuple'>
Type of each phone number is: <class 'str'>
('1234', '1234567890')

print(s.format(employee_id=employee_id, invalid_count=invalid_count))

Employee 1 have 1 invalid phones

s = 'Employee {employee_id} have {invalid_count} invalid phones'
phone_numbers = ['1234', '1234567890']

employee_id, invalid_count = get_invalid_phone_count(1, *phone_numbers) # argument by position works here

Length of phone_numbers is: 2
Type of phone_numbers is: <class 'tuple'>
Type of each phone number is: <class 'str'>
('1234', '1234567890')

print(s.format(employee_id=employee_id, invalid_count=invalid_count))

Employee 1 have 1 invalid phones

Mastering Python

Varying Arguments¶