Python类动态属性访问

Question

I want to access a class attribute by a string with its name.

Something like:

class a:
    b=[]

c='b'
eval('a.'+c+'=1')

But that doesn't work in Python. How can I do this?

Answer 1

Use setattr :

In [1]: class a:
   ...:     b = []
   ...:     

In [2]: setattr(a, 'b', 1)

In [3]: a.b
Out[3]: 1

Use getattr for the reverse:

In [4]: getattr(a, 'b')
Out[4]: 1

In [5]: getattr(a, 'x', 'default')
Out[5]: 'default'

I very much suspect, though, that there is a better way to achieve whatever your goal is. Have you tried using a dictionary instead of a class?

Answer 2

eval is for evaluation, use exec to 'execute' statements:

exec('a.'+c+'=1')

Yet, consider the risk of using both . And you can check out this answer for the difference between expressions and statements.

Since you are looking to set attribute by name, setattr explained in hop's answer is a better practice, and safer than using exec .