理解Python列表理解的问题 [英] Problem in understanding Python list comprehensions

问题描述

以下代码中的最后一行是什么意思?

What does the last line mean in the following code?

import pickle, urllib                                                                                                                                                     

  handle = urllib.urlopen("http://www.pythonchallenge.com/pc/def/banner.p")
  data = pickle.load(handle)
  handle.close()

  for elt in data:
         print "".join([e[1] * e[0] for e in elt])

我对问题的尝试:

• ".join ...使用join方法来清空文本
• e [1] * e [0]将序列中的两个后继值相乘
• 我不确定什么是e
• 我不确定，-loop之前有什么内容，例如:e[1] * e[0] for e in elt

• "".join... uses join -method to empty text
• e[1] * e[0] multiplies two subsequent values in the sequence, e
• I am not sure what is e
• I am not sure, what it means, when you have something before for -loop, like: e[1] * e[0] for e in elt

推荐答案

也许最好用一个例子来解释:

Maybe best explained with an example:

print "".join([e[1] * e[0] for e in elt])

是

x = []
for e in elt:
  x.append(e[1] * e[0])
print "".join(x)

列表推导只是用于for循环的语法糖，它从语句序列中生成表达式.

List comprehensions are simply syntactic sugar for for loops, which make an expression out of a sequence of statements.

elt可以是任意对象，因为您是从泡菜中加载的，e也是如此.用法表明它是序列类型，但可以是实现序列协议的任何东西.

elt can be an arbitrary object, since you load it from pickles, and e likewise. The usage suggests that is it a sequence type, but it could just be anything that implements the sequence protocol.

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