如何检查numpy数组是否已经存在? [英] How can I check whether the numpy array exists already or not?

问题描述

我想知道代码中是否已在某个位置定义了数组.像 a.exist()这样的东西在存在时给出True，在不存在时给出False.

I want to know if an array is already defined somewhere before in the code. Something like a.exist() gives True if it exists and False if it doesn't.

我尝试了 a.size:，但如果该数组尚不存在，则会显示一条错误消息，我想避免.

I tried a.size:, but if the array doesn't exist yet, it gives an error message, which I want to avoid.

如果您想知道的话，要求这样做的情况是循环发生的.

The situation demanding this happened in a loop, if you are wondering.

推荐答案

Python有一些内置函数，如果在当前/本地/全局范围内分配了变量，这些函数可以取消.

Python has some builtin-functions that can ckeck if a variable is assigned in the current/local/global scope.

例如要检查是否在当前本地scopy中定义了变量，请使用:

For example to check if a variable is defined in the current local scopy use:

if 'a' in dir():
    # Variable a is defined.
    if hasattr(a, 'shape'):
        # Probably a numpy array, at least it has a shape.

但这不是很好的python， try/except 更常见，但是出于完整性考虑，我认为值得一提的是，您无需任何try/except就可以做到这一点.

But that's not good python, try/except is more common but for completness I thought it worth mentioning that you can do it without any try/except.

if 'a' in dir():
    print('yes')
else:
    print('no')
# prints 'no' because we haven't defined any variable a

a = np.array([1,2,3])
if 'a' in dir():
    print('yes')
else:
    print('no')
# prints 'yes' because I defined it

del a
if 'a' in dir():
    print('yes')
else:
    print('no')
# prints 'no' because I deleted the variable again

还值得一提的是 locals 和 globals .

Also worth mentioning is locals and globals.

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