Python代码第一次可以正常运行，但是第二次失败

问题描述

我第一次从Notebook运行此代码块时，效果很好:

The first time I run this block of code from Notebook it works fine:

#Which letters and how many
letters = ["a","b","c"]
noOfLetters = len(letters)

#Looking for all permutations
resultA = []
from itertools import permutations
for i in range(noOfLetters):
    resultA.append(list(permutations(letters,i+1)))

如果再次运行它(不重新启动内核)，则会出现以下错误:

If I run it again (without restarting the Kernel) I get the following error:

TypeError                                 Traceback (most recent call last)
<ipython-input-5-4050a4ce7a36> in <module>()
      7 from itertools import permutations
      8 for i in range(noOfLetters):
----> 9     resultA.append(list(permutations(letters,i+1)))

TypeError: 'list' object is not callable

推荐答案

假设笔记本"是Jupyter(以前是ipython笔记本)，则必须注意jupyter保留所有变量的状态.

Assuming "notebook" is Jupyter (previously ipython notebooks), you must be careful that jupyter keeps the state of all variables.

->表示第二次运行从已经初始化为第一次运行结束时具有的值的变量开始.

--> that means that the second run starts with variables already initialized at the value they had at the end of the first run.

避免这种情况的一种方法是重新启动内核.另一个是删除所有变量；另一个是每次运行时都要初始化所有变量.

One way to avoid that is to restart the kernel; another is to delete all variables; one more is to initialize all your variables each time you run.

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