Why Doesn't Print Work in a Lambda

Why doesn't print work in a lambda?

A lambda's body has to be a single expression. In Python 2.x, print is a statement. However, in Python 3, print is a function (and a function application is an expression, so it will work in a lambda). You can (and should, for forward compatibility :) use the back-ported print function if you are using the latest Python 2.x:

In [1324]: from __future__ import print_function

In [1325]: f = lambda x: print(x)

In [1326]: f("HI")
HI

Lambda SNS Not Printing Message

You are not returning anything from your lambda_handler, thus the output is just None. You have to add return statement(s) to your code with actual return values that you want to output from the lambda.

Print statement inside function used within lambda function not executing

Works:

def gen_window(xi, n):
    x, i = xi
    l = []
    for offset in range(n):
        print("-->", (i - offset, (i, x)))
        l.append((i - offset, (i, x)))
    return l

xi = [3,5]
n = 3

gen_window(xi, n)

Lambdas only get executed wenn you actually use them - If you get no output you are probably never using it.

Output:

--> (5, (5, 3))
--> (4, (5, 3))
--> (3, (5, 3))

Use print inside lambda

You can import print_function from the __future__ and use it as a function like this

from __future__ import print_function
map(print, [1, 2, 3])
# 1
# 2
# 3

Why can't we directly print the output of a lambda function/expression directly as a string,list, or tuple?

Your problem has nothing to do with lambda, if you used a function you would run into the same problem - map returns an object, which is an
iterable, ie. it can be converted to a list of values, but it is not a list of values. To print such a list, you must explicitly require its creation:

print(list(map(lambda x: (float(9)/5)*x + 32, Cel)))

Is there a way to perform if in python's lambda?

The syntax you're looking for:

lambda x: True if x % 2 == 0 else False

But you can't use print or raise in a lambda.

---

Related Topics