从10 Most Common Python Mistakes抄来的.

使用 iPython 生成.

#1: 错误的使用表达式做为函数默认值

def foo(a = []):
    a.append('bar')
    return a

foo()
foo()
foo()
foo()




['bar', 'bar', 'bar', 'bar']

#2: 不正确的使用类变量

class A:
    a = 1

class B(A):
    pass

class C(A):
    pass

B.a = 2
print A.a, B.a, C.a
A.a = 3
print A.a, B.a, C.a

1 2 1
3 2 3

#3: 错误的异常块参数

def f():
    #a = None
    try:
        l = [1, 2, 3]
        a = l[100]
    except (ValueError, IndexError) as e:
        pass
    return a

print f()


---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)

<ipython-input-40-ffa24284290f> in <module>()
      8     return a
      9
---> 10 print f()


<ipython-input-40-ffa24284290f> in f()
      6     except (ValueError, IndexError) as e:
      7         pass
----> 8     return a
      9
     10 print f()


UnboundLocalError: local variable 'a' referenced before assignment

#4: 错误的理解Python变量作用域

x = 100
def foo():
    # global x
    x += 101
    print x

foo()

#5: 遍历list时修改了该list

numbers = [x for x in xrange(0, 10)]
for i in numbers:
    if bool(i % 2):
        del numbers[i]

#6: 错误的理解closure的变量绑定

def create_multipliers():
    return [lambda x : x * i for i in range(0, 5)]

for i in create_multipliers():
    print i(2)

#7: 错误的模块依赖

#a.py
import b

def f():
    return b.x

print f()

#b.py
import a

x = 1

def g():
    print a.f()

#8: 命名容易和标准模块混淆

#9: 未注意Python 2 和 Python 3 的差异

#10: 错误的使用del方法

import foo

class Bar(object):
    def __del__(self):
        foo.cleanup(self.myhandle)

#当解释器关闭时, 所有的global 变量都会被设置成None. 所以此时调用__del__会触发AttributeError错误.