How to elegantly access dynamic named variables in Python?

How to efficiently access a series of dynamically named variables in Python programs? For example, we have a set of dictionary variables named tree_1 , tree_2 , tree_n . How do we traverse and access their values?

Using tree_i directly is invalid. The Python interpreter will treat it as a variable named tree_i , rather than tree_1 , tree_2 , etc.

There are two main solutions:

Method 1: Use eval() function

eval() function can execute Python code in the form of a string. We can use a string to format f'tree_{i}' to dynamically generate variable names, and then eval() function converts it to the corresponding variable to get its value.

Sample code:

 tree_1 = {'a1': 1, 'a2': 2}
tree_2 = {'a3': 3, 'a4': 4}
tree_3 = {'a5': 5, 'a6': 6}

for i in range(1, 4):
    tree = eval(f'tree_{i}')
    for key, value in tree.items():
        print(f"tree_{i}: {key} = {value}")

Method 2: Use locals() function

locals() function returns the local variable dictionary of the current scope. We can use f'tree_{i}' as the key to get the corresponding variable value from this dictionary.

Sample code:

 tree_1 = {'a1': 1, 'a2': 2}
tree_2 = {'a3': 3, 'a4': 4}
tree_3 = {'a5': 5, 'a6': 6}

for i in range(1, 4):
    tree = locals()[f'tree_{i}']
    for key, value in tree.items():
        print(f"tree_{i}: {key} = {value}")

Both methods can achieve the same function. However, the eval() function poses a security risk when processing unreliable inputs, so it should be used with caution in scenarios such as processing user input. locals() method is relatively safe. Which method to choose depends on the specific application scenario and security requirements. It is also recommended to use locals() method. Also, a better solution is to use dictionaries or lists to store these variables, avoiding the use of dynamic variable names.

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