Python Projects for Beginners a ten-Week Bootcamp Approach to Python Programming

Filter with Lambdas

Let’s perform the same steps as earlier, except this time we’ll use a lambda function:

# using the filter function with lambda functions, filter out temps below 55F temps = [ 12.5, 13.6, 15, 9.2 ] filtered_temps = list( filter( lambda C : True if (9/5) * C + 32 > 55 else
False, temps) ) # type convert the filter print(filtered_temps)

Go ahead and run the cell. We’ll get the same output as we did earlier, except this time we were able to reduce the number of lines used with our lambda function. The same process that we’re performing can be found in the lines of code in the following:
>>> def convertDeg(degrees):
>>> filtered = [ ] >>> for degree in degrees:
>>> result = (9/5) * degree + 32 >>> if result > 55:
>>> filtered.append(degree)
>>> return filtered
>>> temps = [ 12.5, 13.6, 15, 9.2 ]
>>> filtered_temps = convertDeg(temps)
>>> print(filtered_temps)
Like the map function using lambdas, coupling the filter function with a lambda cuts our code down greatly.
ChapteR 8 advanCed topICs I: eFFICIenCy

The Problem with Reduce

Although I’m going to show you how to use the reduce function, you should understand that there’s a better method than using the actual function. Per the creator of Python himself:
So now reduce( ). This is actually the one I've always hated most, because, apart from a few examples involving + or ∗, almost every time I see a reduce( ) call with a non-trivial function argument, I need to grab pen and paper to diagram what's actually being fed into that function before I understand what the reduce( ) is supposed to do. So in my mind, the applicability of reduce( ) is pretty much limited to associative operators, and in all other cases it's better to write out the accumulation loop explicitly.¹
In his own words, he’s saying that reduce only serves a couple purposes, but other than that, it’s useless, so it makes more sense to use a simple for loop. Let’s look at both examples.
Note Reduce was a built-in function in python 2, since then it has been moved into the functools library.