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HomeBackend DevelopmentPython Tutorial浅谈python新手中常见的疑惑及解答

1 lambda函数

函数格式是lambda keys:express   匿名函数lambda是一个表达式函数,接受keys参数,返回表达式的值。所以不用return,也没有函数名,经常用在需要key参数的函数中,比如sorted。

2 元组(),它是以逗号辨别的,而不是小括号。比如一个元素的元组新手经常写成(12),其实他会被解释成单个元素12.正确的写法应该是(12,),在元素后面加上逗号。

3 模块导入。比如

import random
print random.choice(range(10))

from random import choice
print choice(range(10))

新手会有一种误解,第二种方法只导入了一个函数,而没有把整个模块导入,这是错误的。整个模块其实已经被导入,只是那个函数的引用被保存了起来。所以from-import这种语法不会带来性能上的差异,也没有节省内存。

4 当你有许多module,比如几百个,想要使用时可能会想一个一个导入太麻烦,有没有简便的方法?答案是有的,就是将这些模块组织成一个package。其实就是将模块都放在一个目录里,然后再加一个__init__.py文件,python会将其看作为package,使用里面的函数就可以以dotted-attribute方式来访问。

5 参数传递可变对象是传引用的,不可变对象是传值的。那么什么对象是可变的,什么是不可变的。所有python对象都有三个属性:类型、标识符和值,如果值是可变的就是可变对象,如果值不可变就是不可变对象。像数字、字符串、元组都是不可变对象,剩下的列表、字典、类、类实例等都是可变对象。

6 迭代器的理解,是实现了迭代器协议的容器对象。自己实现一个迭代器,类中要有__iter__()方法,该方法返回一个对象。这个对象要有__next__()方法,在next方法中的适当位置返回StopIteration异常。迭代器不经常使用,所以不用太担心。有替代方法就是生成器。

class MyIterator(object):
  """docstring for MyIterator"""
  def __init__(self, num):
    self.num = num

  def __iter__(self):
    return self;

  def __next__(self):
    if self.num <= 0:
      raise StopIteration;
    
    self.num -= 1;
    return self.num;

for each in MyIterator(5):
  print(each);

-> 结果

7 生成器。函数中只要出现了yield语句就会将其转变成一个生成器。在遇见yield语句后会保存上下文环境,并退出函数。

注意:生成器中没有return语句。

def fun2(num):
  print("start generator");
  while(num>0):
    yield num;
    num -=1;

a=[each for each in fun2(5)]
print(a);->结果
start generator
[5, 4, 3, 2, 1]

学习过程中,难免出错。如果您在阅读过程中遇到不太明白,或者有疑问。

以上这篇浅谈python新手中常见的疑惑及解答就是小编分享给大家的全部内容了,希望能给大家一个参考,也希望大家多多支持脚本之家。

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