How do you iterate through an index in python?
Here's how you can access the indices and array's elements using for-in loops.
1. Looping elements with counter and += operator.
2. Looping elements using enumerate() method.
3. Using index and value separately.
4. You can change the index number to any increment.
5. Automatic counter incrementation with range(len(...)).
6. Using for-in loop inside function.
7. Of course, we can't forget about while loop.
8. yield statement returning a generator object.
9. Inline expression with for-in loop and lambda.
If you’re moving to Python from C or Java, you might be confused by Python’s
In this article I’ll compare Python’s
For loops in other languages
In this loop we:
Looping in Python
Now let’s talk about loops in Python. First we’ll look at two slightly more familiar looping methods and then we’ll look at the idiomatic way to loop in Python.
If we wanted to mimic the behavior of our traditional C-style
This involves the same 4 steps as the
This method of looping in Python is very uncommon.
range of length
I often see new Python programmers attempt to recreate traditional
This first creates a range corresponding to the indexes in our list (
This provides us with the index of each item in our
for-in: the usual way
Both the while loop and range-of-len methods rely on looping over indexes. But we don’t actually care about the indexes: we’re only using these indexes for the purpose of retrieving elements from our list.
Because we don’t actually care about the indexes in our loop, there is a much simpler method of looping we can use:
So instead of retrieving the item indexes and looking up each element, we can just loop over our list using a plain for-in loop.
The other two methods we discussed are sometimes referred to as anti-patterns because they are programming patterns which are widely considered unidiomatic.
What if we need indexes?
What if we actually need the indexes? For example, let’s say we’re printing out president names along with their numbers (based on list indexes).
range of length
We could use
But there’s a more idiomatic way to accomplish this task: use the
This function is meant for solving the task of:
So whenever we need item indexes while looping, we should think of
What if we need to loop over multiple things?
Often when we use list indexes, it’s to look something up in another list.
For example, here we’re looping over two lists at the same time using indexes to look up corresponding elements:
Note that we only need the index in this scenario because we’re using it to lookup elements at the same index in our second list. What we really want is to loop over two lists simultaneously: the indexes just provide a means to do that.
We don’t actually care about the index when looping here. Our real goal is to loop over two lists at once. This need is common enough that there’s a special built-in function just for this.
Looping cheat sheet
Here’s a very short looping cheat sheet that might help you remember the preferred construct for each of these three looping scenarios.
Loop over a single list with a regular for-in:
Loop over multiple lists at the same time with
Loop over a list while keeping track of indexes with
If you find yourself tempted to use
In fact, if you find yourself reaching for
If you find yourself struggling to figure out the best way to loop, try using the cheat sheet above.
Practice makes perfect
You don’t learn by putting information in your head, you learn by attempting to retrieve information from your head. So you’ve just read an article on something new, but you haven’t learned yet.
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How do you iterate through a list in Python index?
Loop through a list with an index in Python.
Using enumerate() function. The Pythonic solution to loop through the index of a list uses the built-in function enumerate(). ... .
Using range() function. Another way to iterate over the indices of a list can be done by combining range() and len() as follows: ... .
Using zip() function..
How do you start a for loop from a specific index in Python?
Use slicing to start a for loop at index 1 Use slice notation [start:] with start as 1 to create a copy of the sequence without the element at index 0 . Iterate over the sliced sequence. To start the loop at an element at a different index, set start to the desired index.
How will a loop variable iterate over the index values of a list?
You can access the index even without using enumerate() ..
Using a for loop, iterate through the length of my_list . Loop variable index starts from 0 in this case..
In each iteration, get the value of the list at the current index using the statement value = my_list[index] ..
Print the value and index ..
How do you use the index function in Python?
Syntax of index() Method.
Syntax: list_name.index(element, start, end).
Return: Returns the lowest index where the element appears..
Error: If any element which is not present is searched, it raises a ValueError..