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Table of Contents
Position parameters are the most basic usage
Keyword parameters make calls clearer
Default parameter values ??simplify common scenarios
*args and **kwargs handle uncertain number of parameters
Home Backend Development Python Tutorial Python Function Arguments and Parameters

Python Function Arguments and Parameters

Jul 04, 2025 am 03:26 AM
python parameter

Parameters are placeholders when defining a function, while arguments are specific values ??passed in when calling. 1. Position parameters need to be passed in order, and incorrect order will lead to errors in the result; 2. Keyword parameters are specified by parameter names, which can change the order and improve readability; 3. Default parameter values ??are assigned when defined to avoid duplicate code, but variable objects should be avoided as default values; 4. args and *kwargs can handle uncertain number of parameters and are suitable for general interfaces or decorators, but should be used with caution to maintain readability.

Python Function Arguments and Parameters

When writing Python functions, parameters and arguments are often a bit confusing, especially when I first started learning. In fact, figuring out the differences and usage between them is very helpful for writing flexible and clear functions.

Python Function Arguments and Parameters

Position parameters are the most basic usage

The parameters written when defining a function are "parameters", and the values ??passed in when calling the function are "arguments". for example:

Python Function Arguments and Parameters
 def greet(name, message):
    print(f"{message}, {name}!")

greet("Alice", "Hello")

Here name and message are parameters, while "Alice" and "Hello" are the actual parameters passed. The order is very important, and if you reverse it, the result may be wrong.

A common mistake is to confuse the parameter order, especially when the parameter names are not very intuitive. It is recommended to give a better name, not use a, b, and c, as it is easy to make mistakes.

Python Function Arguments and Parameters

Keyword parameters make calls clearer

When calling a function, you can use keywords to specify the parameter name, so that even if the order changes, the result will not be affected:

 greet(name="Bob", message="Hi") # equivalent to greet("Bob", "Hi")

This method is particularly suitable for situations where there are many parameters or some parameters have default values. It allows you to see which value corresponds to which parameter at a glance, improving code readability.

The benefits of using keyword parameters include:

  • It's easier to understand: others will know what you're setting up at a glance
  • You can skip parameters with default values
  • Adjustment order does not affect execution results

But don't abuse it. If you write too long keywords, you will lose money if you want.


Default parameter values ??simplify common scenarios

Set a default value for the parameters, and in many cases you can write less duplicate code:

 def greet(name, message="Hello"):
    print(f"{message}, {name}!")

greet("Tom") # Use default values ??greet("Tom", "Hey") # Override default values

This technique is very practical, but a few things to note:

  • The default value is only calculated once when defining a function. Do not use mutable objects (such as lists or dictionaries) as the default value.
  • Put the commonly used parameters in front, put the uncommonly used parameters behind and set the default value
  • If multiple parameters have default values, try to sort them in logical order

For example, be careful when writing the following:

 def add_item(item, lst=[]): # This is not recommended to write lst.append(item)
    return lst

Because the default list will only be created once, multiple calls will share the same list, which may lead to unexpected behavior.


*args and **kwargs handle uncertain number of parameters

Sometimes you don’t know how many parameters you want to pass. At this time, you can use *args and **kwargs to handle any number of positional parameters and keyword parameters.

 def print_args(*args, **kwargs):
    print("Positional:", args)
    print("Keyword:", kwargs)

print_args(1, 2, name="Alice", age=30)

This writing method is often used to encapsulate functions, decorators, or general interfaces. The advantage is that it can accept various inputs without reporting errors.

But also note:

  • Try to avoid overuse in the end user interface, otherwise readability will decrease
  • Use fixed parameters in clear cases
  • Adding type prompts to *args and **kwargs can help maintain

Basically that's it. The parameters part looks simple, but if used properly, it can make the function both flexible and clear. On the other hand, if used randomly, it is easy to write confusing code.

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