[Python] Arguments

• We need to be careful using mutable default arguments when defining our functions
• The same argument will be called again when doing multiple function calls, resulting in an error
• To avoid this matter, we can use None as a special value to indicate we did not receive anything and instantiate a new empty list

def createStudent(name, age, grades=None):
  if grades is None:
    grades = []
  return {
    'name': name,
    'age': age,
    'grades': grades
  }
 
def addGrade(student, grade):
    student['grades'].append(grade)
    # To help visualize the grades we have added a print statement
    print(student['grades'])

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*args and **kwargs

We can use *args(non-keyword arguments) and **args(keyword arguments) to define our function parameters

 

Function arguments are accepted in the following order in the function parameter:

1. Standard positional arguments
2. *args
   •  non-keyword arguments / positional arguments in a function call are mapped to an args tuple.
3. Standard keyword arguments
4. **kwargs
   • keyword arguments in a function call are mapped to an args dictionary
   • we can use dictionary operations on the keyword arguments

def print_animals(animal1, animal2, *args, animal4, **kwargs):
  print(animal1, animal2)
  print(args)
  print(animal4)
  print(kwargs)

print_animals('Snake', 'Fish', 'Guinea Pig', 'Owl', animal4='Cat', animal5='Dog')
#output
#Snake Fish
#('Guinea Pig', 'Owl')
#Cat
#{'animal5': 'Dog'}

 

def assign_food_items(**order_items):
  food = order_items.get('food')
  drinks = order_items.get('drinks')
  print(food)
  print(drinks)

# Example Call
assign_food_items(food='Pancakes, Poached Egg', drinks='Water')
#output
# Pancakes, Poached Egg
# Water

 

We can apply *args and **args for function calls as well

my_num_list = [3, 6, 9]
numbers  = {'num1': 3, 'num2': 6, 'num3': 9}

def sum(num1, num2, num3):
  print(num1 + num2 + num3)
 
sum(*my_num_list)
sum(**numbers)
#output is 18 for both cases

 

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