Why Do Lambda Functions in a Loop All Refer to the Same Variable?

Lambda Function Behavior in Loop

In the given code snippet, a dictionary is being populated with lambda functions. Each function is responsible for changing the current directory to a特定名称. However, when the loop completes, all lambda functions reference the same directory name.

To understand why this occurs, it is critical to recognize the nature of lambda functions in loops. Lambda functions are closures, meaning they capture the values of their enclosing scope. In this case, the lambda function is defined within the loop and captures the value of the d variable.

However, the d variable is being reused throughout the loop, continuously overwriting its value. As a result, all lambda functions end up capturing the same final value of d.

Solution

To resolve this issue, it is necessary to bind each lambda function to a specific value of d. This can be achieved by using a default parameter value:

lambda d=d: self.root.change_directory(d)

In this code, the lambda function takes an optional parameter d with a default value of the current value of d in the loop. Since default parameter values are evaluated when the function is created, each lambda function will capture its own unique value of d.

Alternatively, an additional closure can be used to achieve the same result:

(lambda d: lambda: self.root.change_directory(d))(d)

In this case, an outer lambda function is used to create a closure around the d variable. The inner lambda function is then used to perform the directory change.

By utilizing these techniques, it is possible to ensure that each lambda function in the loop has its own unique binding to the d variable, resulting in the desired behavior.

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