Lambda Functions

It's best to start off with some examples:

Example 1:

my_list = range(26)

print(my_list)
print(filter(lambda x: x % 2 == 0, my_list))

Breaking down the first example:


lambda - the keyword to create a lambda
x - the parameter. Multiple parameters ex: lambda x,y,z:
x % 2 == 0: the execution code
my_list: the argument. Multiple args ex: lambda x,y,z: <code>, input1, input2, key

Multiple arg/param lambda: 
lambda x,y,z: (x + y) - z, input1, input2, key

Example 2:

g = lambda x,y: x>y
print g(1,2)
print g(2,1)

As you can tell, lambdas appear to be shortened functions; specifically one lined functions. And while this is true to an extent... that is not their purpose.

Lambdas, in short, are anonymous functions. Functions without a name. They are generally passed as arguments to higher-order functions as well as a variety of other uses. Below are some of the features of a Lambda

Lambda Features:

Lambda forms can take any number of arguments
Return only one value in the form of an expression
They cannot contain commands or multiple expressions
It cannot be a direct call to print because lambda requires an expression
Lambda functions have their own namespace

Due to the fact that they have their own local namespace... Lambdas cannot access variables other than those in their parameters list and globals.

Example:

def factorial(n):return reduce(lambda x,y:x*y,[1]+range(1,n+1))

Breakdown of a Lambda

#Define a regular function
def reg_function(x):
    return x**2

# Make it one line
def reg_function(x): return x**2

# Turn it into a lambda
new_stuff = lambda x: x**2

Common Lambda Uses

map()

Map applies a function to all the items in an input_list. That function can be a lambda.

filter()

Filter creates a list of elements for which a function returns true.

reduce()

Reduce accepts a function and a sequence and returns a single calculated value.

Examples

Continue to Performance Labs: 4A and 4B

Python