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Iterating with Enumerate
4:24Learn about the enumerate function, another tool to iterate over sequences.
Cool, we've seen how basic for
loops work in Python.
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We can iterate through a sequence and
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access each element of that
sequence individually.
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In this video,
we're gonna be expanding on the for
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loop a little bit to talk
about the enumerate function.
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The enumerate function comes in
handy when we need to know the index
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of the current element in our loop.
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Or we want some kind of counter.
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Let's look at this grocery
list example again.
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We have this list, and that's all well and
good, but I want it to print out nice, and
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neat, and numbered.
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How do I get the numbers?
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Well, here's one potential option
that we're going to explore and
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then improve on.
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So, first we can create a variable
to store our counter number.
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We'll assign the integer one to it
because most grocery lists start at one.
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Then we have our for
loop here from the previous example.
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But I'm gonna edit the print statement so
that it prints out the index variable too.
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I'm gonna use an f-string to do this.
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An f-string is something we can use
in Python to help us print variables
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inside of strings.
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To use one,
you type the letter f before your string.
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Then when you want to insert a variable,
you simply include it inside your string,
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surrounded by curly braces.
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F-strings are new in Python three and
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won't work if you're
running an earlier version.
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So I'm gonna add the index
variable in here too.
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So that print statement is printing
out the value of the index variable.
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Followed by a period, then a space, and
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then the value of our item variable,
which is the current element in the loop.
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Then finally, I'll increase the value
of the index variable by one.
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Now, if we run this we'll see a neat and
numbered grocery list.
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Let's check.
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Cool, this works, but
this approach is not very Pythonic.
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Mostly because Python provides a built in
function that does this exact same thing
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for us in a much cleaner way.
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This function is called enumerate.
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Enumerate takes two arguments,
an iterable and
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an optional argument that defines
a starting counter number.
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It returns what the Python
docs call an enumerate object.
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You'll learn all about
objects in later material.
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But for now just understand that, when you
call this Python function in a for loop,
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you get back both the index
of the current element along
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with the current element itself.
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So, to use the enumerate function,
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we'll replace the reference to
the groceries list with a call to
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the enumerate function where we pass
the groceries list as an argument to it.
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Now we'll change our item
variable in the loop to a tuple.
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This is one of those handy spots
where we can use multiple assignment.
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Finally we can get rid of the old
references to the index variable,
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we don't need them anymore.
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And that's it.
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The current item in the grocery list
will be assigned to the item variable.
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And its corresponding index will
be assigned to the index variable.
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If we run this,
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we'll see that we get a really similar
output to our first approach, let's check
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Okay, it's pretty close but we don't
want a grocery list that starts at zero.
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Sure, Python sequences
start with index zero, but
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most lists written by humans don't.
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The enumerate function accounts for this
with that optional argument I mentioned.
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Let's pass a second argument to
the enumerate function, the number 1.
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This tells enumerate to start the counter
at 1, instead of the default of 0.
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Now if we save and run this again, we
should have the lists we're looking for.
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Cool, looking good.
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Now, just so you know, the optional
argument will take any valid integer.
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If for some curious reason we wanted
the grocery list to start at 20,
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we could do that too.
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Let's check it out.
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Cool, all right.
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Great work, everyone.
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See you in the next video.
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