Common Gotchas

1. Mutable default arguments

   A new list is created once when the func is defined, and the same list is used in each successsive call: Python's default arguments are evaluated once when the func is defined, not each time the func is called.

   This means that if you use a mutable default argument and mutate is, you will have mutated that object fro all future calls to the function as well.

   
   image.png
   image.png
   

   (But sometimes this gotcha could not be a gotcha,for instance,you want to maintain state between calls of a function like cache)

2. Late binding closures

image.png

What you you should do instead
the one:

image.png
the two:

image.png

3. Python package name can not contains '-' character

4. 在对一个list进行pop操作时，必须是按逆序来删除。即，先删下标大的元素，再删下标小的元素，否则 会越界。

5.在使用sorted对iterable进行排序的时候，并不会改变传进来的iterable。而是生成一个新的排序好的iterable并return。

num = 1
def t():
    print(num)
    # 在进行赋值操作时，解释器默认变量为本地变量
    num += 1

t()

解决办法 声明 global num

7. decimal module. https://www.v2ex.com/t/415039

8, 解决 Windows 下 Python 的 too many file descriptors in select() 报错