Lambda expression in a Loop
Suppose we have a loop that creates a list of lambda functions, each with a different value of a variable. In the below example, we have defined a list “lambdas” which is then populated with five lambda functions, each with a different value of i. However, when the lambda functions are executed in the second loop, they all return the same value of 4, which is the final value of “i” in the first loop. This is because the lambda functions are all using the same value of “i”, which has been closed over and is now part of their environment.
Python3
# Defining a list named lambdaslambdas = []# Running a loop which append values to list# lambdas by calling create_lambda() functionfor i in range(5): lambdas.append(lambda :i)# Printing the items of list lambdasfor l in lambdas: print(l()) |
Output:
4 4 4 4 4
This behavior can be confusing and unexpected, especially if you are not aware of the way that lambda functions capture variables. It can also be difficult to debug, as the lambda functions may appear to be correct when they are defined, but produce unexpected results when they are executed.
To understand why this happens, it is important to realize that lambda functions are defined and executed at different times. When the lambda functions are defined in the first loop, they capture the current value of the “i” variable, which is updated in each iteration of the loop. However, the lambda functions are not executed until the second loop, at which point they all use the final value of “i”, which is 4.
Why do Python lambda defined in a loop with different values all return the same result?
In this article, we are going to learn why Python lambda defined in a loop with different values all return the same result.
In this article, we will explore the reasons behind this behavior and discuss how to avoid it. We will start by looking at how lambda functions are defined and executed, and how they capture the values of variables that are used within their body. We will then look at an example of how this can cause lambda functions defined in a loop to all return the same result, and finally, we will discuss how to avoid this issue by using default argument values instead of closing over variables.