Why can't Python's lambda expressions contain statements?

Yes, Python Lambda expressions cannot contain statements. Before we delve into the reasons, let’s understand what Lambda is, its expressions and statements.

Lambda expressions allow the definition of anonymous functions. A Lambda function is an anonymous function without a name. Let’s look at the syntax −

lambda arguments: expressions

The keyword lambda defines a lambda function. A lambda expression contains one or more parameters, but it can only have one expression.

Lambda Example

Let’s look at an example −

myStr = "Thisisit!"
(lambda myStr : print(myStr))(myStr)

Output

Thisisit!

Use Lambda to sort a list based on the value of another list

In this example, we will sort the list based on the values ​​of another list, i.e. the second list will be sorted by their index in the sorted order -

# Two Lists
list1 = ['BMW', 'Toyota', 'Audi', 'Tesla', 'Hyundai']
list2 = [2, 5, 1, 4, 3]

print("List1 = \n",list1)
print("List2 (indexes) = \n",list2)

# Sorting the List1 based on List2
res = [val for (_, val) in sorted(zip(list2, list1), key=lambda x: x[0])]
print("\nSorted List = ",res)

Output

List1 = 
 ['BMW', 'Toyota', 'Audi', 'Tesla', 'Hyundai']
List2 (indexes) = 
 [2, 5, 1, 4, 3]

Sorted List =  ['Audi', 'BMW', 'Hyundai', 'Tesla', 'Toyota']

Lambda expressions cannot contain statements

We saw two examples of using Lambda expressions above. Python's Lambda expressions cannot contain statements because Python's syntax framework cannot handle statements nested within expressions.

In Python, functions are already first-class objects and can be declared in local scope. So the only advantage of using a lambda instead of defining the function locally is that you don't need to give the function a name, i.e. an anonymous function, but it's just a local variable that is assigned to the function object!

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