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[Jose]-Hi and welcome back.

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In this video we are talking about the map function.

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In the last video we briefly mentioned when you would use

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filter, or when would you use generator comprehensions.

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And so I wanted to just quickly say, "that you'll use filter

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"when you are programming with people, who haven't been

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"programming in Python for very long."

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For example, programmers from other programming languages,

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or just when your project involves

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multiple programming languages.

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Python is one of the few programming languages

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that has syntax like this.

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So if you are working with many programming languages,

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maybe make sense to use the filter function,

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and that way, keep everything consistent.

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Use the filter function

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throughout all the languages you use.

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Also, you'll use the filter function

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if you have a function already defined,

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and you don't have to create one.

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That way it can be a bit faster.

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Finally, there is also something to say for this variable

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that we are creating here in this comprehension.

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This variable is pretty pointless, so there is something

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to be said for not creating this variable here.

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It's up to you which one you go for,

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but the main way of deciding, I would say,

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is whether your programming

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with other people who like filter function,

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instead of comprehensions.

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If you're only programming with Python developers

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use comprehensions, and if they don't like it

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get them to like it, for it will generally be better.

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Okay, that's enough of that.

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Let's talk about the map function.

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The map function is used to take an iterable,

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and output an new iterable, where each element

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has been modified according to some function.

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Let's take for example, this map here.

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Friends_lower is going to map(lambda x: x.lower,

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of friends).

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Again, very similar to the filter function.

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It also takes a function of the start

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that returns something and takes something

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as a barometer, and what it takes is each

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of the elements of this iterable here.

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So the first one is Rolph and returns Rolph

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all in lower case letters.

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Then it takes Jose and returns in all

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in lower case letters and so forth.

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But it produces a generator.

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So the first time you call "next", you get Rolph,

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with all lower case.

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Let's do that.

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And as you can see, you get Rolph,

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all in lower case there.

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This is very identical to this list comprehension here.

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Friend lower for friend in friends,

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and it's of course identical,

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to this friends_lower generator comprehension,

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like so.

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Which one should you use?

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This one, the generator comprehension,

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unless you need them all to be in a list,

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then you can do this list comprehension.

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When should you use map?

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Again, like I said earlier, when the people

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in your team, the people you are working with,

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are accustomed to using map, that's very popular

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in other programming languages,

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or when you're working with other programming languages

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at the same time, and you want to keep

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everything consistent, or when you think its gonna

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be more readable because some of the functions

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you've got defined earlier on you can use without

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having to create the new lambda function.

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So here's an example of another point in time,

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where you may use map instead of filter.

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Let's say we've got a class User: that defines

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and init method, and including a username

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and password.

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And then it's got a classmethod

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that is from _dict.

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So given a dictionary of data, it's going

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to return a user object.

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So it's going to return cls of data username,

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and data password, for example.

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Okay.

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Now you've got this defined here in the user class,

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and given that you have a list of users like this one,

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I'm going to copy them from my notes, just so

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I don't bore you typing them out.

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You've got Rolf and tecladoisawesome,

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and youaretoo is the password.

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Given that you have this from_dict function here,

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and you wanted to create a list of user objects

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from these dictionaries, you could do

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something like this.

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And that is User.from_dict(user) for,

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sorry this should be users list, by the way,

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my apologies, for user in users,

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and that will be fine.

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But I actually feel that a map could be more readable.

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It's also a bit shorter, but that's beside the point.

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I just think this is more readable here,

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because you know that you're calling this from.dict

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function for each element in this iterable.

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Whereas the list comprehension, you sort

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of have to read it, and you have to create this

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new variable that is only used for iteration

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and nothing else, and you're actually calling this

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function here, I don't know, I just feel like

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the map in this case is a bit more readable.

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So, keep that in mind, if you feel that way too,

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that sometimes map can be a better choice

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than list comprehension.

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And that's just an example there.

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So that's it for this video, hope you've learned

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something about the map function,

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and I'll see you on the next video.