Function Arguments¶
You can include as many arguments as you want in your function definition. Inside the function, these arguments can be treated as variables.
def arg3(arg1, arg2, arg3):
print(arg1)
print(arg2)
return arg3
arg3(1, 2, 3)
1
2
3
You may use variables or statements (anything that resolves to a value or object) as arguments:
var1 = 45
arg3(var1, 3*4, 7)
45
12
7
Positional Arguments¶
The arguments defined above are called positional arguments. In order to set them correctly, you need to parse them in the order they are defined in the function. You must also provide a value for each argument:
arg3('a', 'b')
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-4-964cf24ab02e> in <module>
----> 1 arg3('a', 'b')
TypeError: arg3() missing 1 required positional argument: 'arg3'
Keyword Arguments¶
If you want to set optional arguments with a default value, you can use keyword arguments. The syntax is:
def function_name(keyword_arg = default_value):
For example:
def hello(name = 'World', time = 'today'):
return f'Hello {name}! How are you {time}?'
(If you are unfamiliar with f-strings f'', see the page on The Python Standard Library/Strings/String Formatting)
This function can be called with no arguments, in which case the default values will be used:
hello()
'Hello World! How are you today?'
We can also parse the arguments like positional arguments:
hello('reader', 'feeling')
'Hello reader! How are you feeling?'
hello('reader')
'Hello reader! How are you today?'
Keyword arguments can be referred to by name, and out of order:
hello(time = 'this morning')
'Hello World! How are you this morning?'
Combining Positional and Keyword Arguments¶
If you define a function with both positional and keyword arguments, the positional arguments must appear before the keyword arguments.
For example:
def hello_hello(num, name = 'World', time = 'today', weather = 'good'):
return f"Hello {num*'hello'} {name}! How are you {time}?"
Here the positional argument num must be provided
hello_hello()
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-11-260a0f5fbf0a> in <module>
----> 1 hello_hello()
TypeError: hello_hello() missing 1 required positional argument: 'num'
As before, the keyword arguments can be provided like positional arguments or by name:
hello_hello(1, 'there', 'doing')
'Hello hello there! How are you doing?'
hello_hello(0, time = 'awake this early', name = 'sleepy head')
'Hello sleepy head! How are you awake this early?'