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python - How do I create variable variables?

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菜鸟教程小白 发表于 2022-4-10 15:39:39 | 显示全部楼层 |阅读模式 打印 上一主题 下一主题

How do I accomplish variable variables in Python?

Here is an elaborative manual entry, for instance: Variable variables

I hear this is a bad idea in general though, and it is a security hole in PHP. Is that true?



推荐答案

You can use dictionaries to accomplish this. Dictionaries are stores of keys and values.

>>> dct = {'x': 1, 'y': 2, 'z': 3}
>>> dct
{'y': 2, 'x': 1, 'z': 3}
>>> dct["y"]
2

You can use variable key names to achieve the effect of variable variables without the security risk.

>>> x = "spam"
>>> z = {x: "eggs"}
>>> z["spam"]
'eggs'

For cases where you're thinking of doing something like

var1 = 'foo'
var2 = 'bar'
var3 = 'baz'
...

a list may be more appropriate than a dict. A list represents an ordered sequence of objects, with integer indices:

lst = ['foo', 'bar', 'baz']
print(lst[1])           # prints bar, because indices start at 0
lst.append('potatoes')  # lst is now ['foo', 'bar', 'baz', 'potatoes']

For ordered sequences, lists are more convenient than dicts with integer keys, because lists support iteration in index order, slicing, append, and other operations that would require awkward key management with a dict.

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