python 反模式
2016-08-01 08:17
120 查看
不使用 pythonic 的循环:
l = [1,2,3] #Bad for i in range(0,len(list)): le = l[i] print(i,le) #Good for i,le in enumerate(l): print(i,le)
函数调用返回一个以上的变量类型
#Bad def filter_for_foo(l): r = [e for e in l if e.find("foo") != -1] if not check_some_critical_condition(r): return None return r res = filter_for_foo(["bar","foo","faz"]) if res is not None: #continue processing pass #Good def filter_for_foo(l): r = [e for e in l if e.find("foo") != -1] if not check_some_critical_condition(r): raise SomeException("critical condition unmet!") return r try: res = filter_for_foo(["bar","foo","faz"]) #continue processing except SomeException: #handle exception
循环永不终止
#example: i = 0 while i < 10: do_something() #we forget to increment i
不使用 .iteritems() 遍历 dict 的键/值对.
#Bad d = {'foo' : 1,'bar' : 2} for key in d: value = d[key] print("%s = %d" % (key,value)) #Good for key,value in d.iteritems(): print("%s = %d" % (key,value))
不使用 zip() 遍历一对列表
#Bad l1 = [1,2,3] l2 = [4,5,6] for i in range(l1): l1v = l1[i] l2v = l2[i] print(l1v,l2v) #Good for l1v,l2v in zip(l1,l2): print(l1v,l2v)
Using "key in list" to check if a key is contained in a list.
This is not an error but inefficient, since the list search is O(n). If possible, a set or dictionaryshould be used instead.
Note: Since the conversion of the list to a set is an O(n) operation, it should ideally be done only once when generating the list.
#Bad: l = [1,2,3,4] if 3 in l: pass #Good s = set(l) if 3 in s: pass
在循环之后,不使用 'else'.
#Bad found = False l = [1,2,3] for i in l: if i == 4: found = True break if not found: #not found... pass #Good for i in l: if i == 4: break else: #not found...
对于dict,不使用.setdefault()设置初始值
#Bad d = {} if not 'foo' in d: d['foo'] = [] d['foo'].append('bar') #Good d = {} foo = d.setdefault('foo',[]) foo.append(bar)
对于dict,不使用.get()返回缺省值
#Bad d = {'foo' : 'bar'} foo = 'default' if 'foo' in d: foo = d['foo'] #Good foo = d.get('foo','default')
使用map/filter而不是列表解析
#Bad: values = [1,2,3] doubled_values = map(lambda x:x*2,values) #Good doubled_values = [x*2 for x in values] #Bad filtered_values = filter(lambda x:True if x < 2 else False,values) #Good filtered_values = [x for x in values if x < 2]
不使用defaultdict
#Bad d = {} if not 'count' in d: d['count'] = 0 d['count']+=1 #Good from collections import defaultdict d = defaultdict(lambda :0) d['count']+=1
从一个函数中返回多个值时,不使用命名元组(namedtuple)
命名元组可以用于任何正常元组使用的地方,但可以通过name访问value,而不是索引。这使得代码更详细、更容易阅读。#Bad def foo(): #.... return -1,"not found" status_code,message = foo() print(status_code,message) #Good from collections import namedtuple def foo(): #... return_args = namedtuple('return_args',['status_code','message']) return return_args(-1,"not found") ra = foo() print(ra.status_code,ra.message)
不使用序列的显式解包
支持解包的序列有:list, tuple, dict#Bad l = [1,"foo","bar"] l0 = l[0] l1 = l[1] l2 = l[2] #Good l0,l1,l2 = l
不使用解包一次更新多个值
#Bad x = 1 y = 2 _t = x x = y+2 y = x-4 #Good x = 1 y = 2 x,y = y+2,x-4
不使用'with'打开文件
#Bad f = open("file.txt","r") content = f.read() f.close() #Good with open("file.txt","r") as input_file: content = f.read()
要求许可而不是宽恕
#Bad import os if os.path.exists("file.txt"): os.unlink("file.txt") #Good import os try: os.unlink("file.txt") except OSError: pass
不使用字典解析
#Bad l = [1,2,3] d = dict([(n,n*2) for n in l]) #Good d = {n : n*2 for n in l}
使用字符串连接,而不是格式化
#Bad n_errors = 10 s = "there were "+str(n_errors)+" errors." #Good s = "there were %d errors." % n_errors
变量名包含类型信息(匈牙利命名)
#Bad intN = 4 strFoo = "bar" #Good n = 4 foo = "bar"
实现java风格的getter和setter方法,而不是使用属性。
#Bad class Foo(object): def __init__(a): self._a = a def get_a(self): return a def set_a(self,value): self._a = value #Good class Foo(object): def __init__(a): self._a = a @property def a(self): return self._a @a.setter def a(self,value): self._a = value #Bad def calculate_with_operator(operator, a, b): if operator == '+': return a+b elif operator == '-': return a-b elif operator == '/': return a/b elif operator == '*': return a*b #Good def calculate_with_operator(operator, a, b): possible_operators = { '+': lambda a,b: a+b, '-': lambda a,b: a-b, '*': lambda a,b: a*b, '/': lambda a,b: a/b } return possible_operators[operator](a,b) #Bad class DateUtil: @staticmethod def from_weekday_to_string(weekday): nameds_weekdays = { 0: 'Monday', 5: 'Friday' } return nameds_weekdays[weekday] #Good def from_weekday_to_string(weekday): nameds_weekdays = { 0: 'Monday', 5: 'Friday' } return nameds_weekdays[weekday]
相关文章推荐
- C++ Boost 之Python(生成一个扩展模块)
- Python指南--数据结构
- Python指南--数据结构
- 搭建Python的集成开发环境WingIDE
- Python指南--深入流程控制
- Python指南--深入流程控制
- 用Python实现数据库编程
- Python指南--开胃菜
- Python指南--开胃菜
- Python指南--初步认识Python
- Python指南--初步认识Python
- Python指南--前言
- Python指南--使用Python解释器
- Python指南--使用Python解释器
- Python指南--前言
- python库lxml在linux和WIN系统下的安装
- C++ Boost 之Python(一个简单的例子)
- C++ Boost 之Python(继承)
- C++ Boost 之Python(大纲)