Python函数定义与调用：字符串参数引号使用差异疑问

Hey there! Awesome question—this is such a fundamental point that trips up lots of new Python learners, so let's unpack it step by step.

First, let's clarify the two entirely different things you're looking at:

1. Function parameter names (like word in def shout(word):) #

When you define a function, word is just a variable placeholder. Think of it as a label that says, "When someone calls this function, whatever value they send me will go into this label, and I can use it inside the function."

In Python, variable names never need quotes. If you tried writing def shout('word'):, Python would throw an error immediately—because it expects a variable name here, not a literal string. The parameter name is just a way to refer to the value that will later be passed in, not the value itself.

2. String arguments (like 'abd' in shout('abd')) #

When you call the function, 'abd' is a string literal—that's the actual text value you want to pass to the function. Python uses quotes to tell the difference between:

• A piece of text (like the word "abd" itself)
• A variable name (like if you had previously defined abd = 'hello', then shout(abd) would pass the value stored in the abd variable, no quotes needed)

If you forgot the quotes and wrote shout(abd), Python would look for a variable named abd—if you hadn't defined one, you'd get a NameError because it can't find that variable.

Quick example to drive this home #

Let's say you do this:

my_favorite_word = 'python'
shout(my_favorite_word)

Here, my_favorite_word is a variable name (no quotes), just like the word parameter in the function definition. We're passing the value that my_favorite_word points to ('python') into the function.

To sum it up:

• Parameter names = labels for future values → no quotes needed
• String literals = actual text values → quotes required to tell Python "this is a string, not a variable name"

内容的提问来源于stack exchange，提问作者Shiqi Zhang