freeCodeCamp/guide/chinese/python/defining-functions/index.md

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---
title: Python Defining Functions
localeTitle: Python定义函数
---
[Python文档](https://docs.python.org/3/tutorial/controlflow.html#defining-functions)
我们可以创建一个将Fibonacci系列写入任意边界的函数
```
>>> def fib(n): # write Fibonacci series up to n
... """Print a Fibonacci series up to n."""
... a, b = 0, 1
... while a < n:
... print(a, end=' ')
... a, b = b, a+b
... print()
...
>>> # Now call the function we just defined:
... fib(2000)
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
```
[`def`](https://docs.python.org/3/reference/compound_stmts.html#def)关键字引入了函数定义。它必须后跟函数名称和带括号的形式参数列表。构成函数体的语句从下一行开始,必须缩进。
函数体的第一个语句可以选择是字符串文字;此字符串文字是函数的文档字符串或[docstring](https://www.python.org/dev/peps/pep-0257/) (有关文档[字符串的](https://www.python.org/dev/peps/pep-0257/)更多信息请参阅文档字符串部分。有些工具使用文档字符串自动生成在线或印刷文档或让用户以交互方式浏览代码。在你编写的代码中包含docstrings是一种很好的做法所以尽量养成习惯。