函数

In [1]: def check_num(num, ignore=False):
   ...:     if ignore:
   ...:         return
   ...:
   ...:     if num < 0:
   ...:         print("num < 0")
   ...:     elif num == 0:
   ...:         print("num == 0")
   ...:     else:
   ...:         print("num > 0")
   ...:

In [2]: check_num()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-e2de90bec545> in <module>
----> 1 check_num()

TypeError: check_num() missing 1 required positional argument: 'num'

In [3]: check_num(1)
num > 0

In [4]: check_num(2)
num > 0

In [5]: check_num(2, ignore=True)

In [6]: check_num(2, True)

如果 return 后面不接返回值，那么默认将会返回 None。

函数

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