Python：迭代时将元素添加到列表中 [英] Python: Adding element to list while iterating

问题描述

我知道在迭代列表时不允许删除元素，但允许在迭代时将元素添加到python列表中。这是一个例子：

I know that it is not allowed to remove elements while iterating a list, but is it allowed to add elements to a python list while iterating. Here is an example:

    for a in myarr:
      if somecond(a):
          myarr.append(newObj())

我在我的代码中尝试了这个并且似乎工作正常，但是我不知道是不是因为我很幸运，并且它将来会在某个时候破裂？

I have tried this in my code and it seems to works fine, however i dont know if its because i am just lucky and that it will break at some point in the future?

编辑：我不想复制列表，因为myarr是巨大的，因此它会太慢。另外我需要用somecond（）来检查附加的对象。

i prefer not to copy the list since "myarr" is huge, and therefore it would be too slow. Also i need to check the appended objects with "somecond()".

编辑：在某些时候somecond（a）将是假的，所以不可能无限循环。

At some point "somecond(a)" will be false, so there can not be an infinite loop.

编辑：有人问过somecond（）函数。 myarr中的每个对象都有一个大小，每次somecond（a）为真，并且新对象被附加到列表中，新对象的大小将小于a。 somecond（）有一个epsilon表示小对象可以如何，如果它们太小则会返回false

Someone asked about the "somecond()" function. Each object in myarr has a size, and each time "somecond(a)" is true and a new object is appended to the list, the new object will have a size smaller than a. "somecond()" has an epsilon for how small objects can be and if they are too small it will return "false"

推荐答案

您可以使用itertools中的 islice 在列表的较小部分上创建迭代器。然后你可以在不影响你迭代的项目的情况下将条目附加到列表中：

You could use the islice from itertools to create an iterator over a smaller portion of the list. Then you can append entries to the list without impacting the items you're iterating over:

islice( myarr, 0, len(myarr)-1 )

更好的是，你甚至不必遍历所有元素。您可以增加步长。

Even better, you don't even have to iterate over all the elements. You can increment a step size.

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