Iterate over a list in Python
- List is like arrays in other languages, with the extra advantage of being dynamic in size. In Python, the list may be a sort of container in Data Structures, which is used to store multiple data at the same time. Unlike Sets, lists in Python are ordered and have a definite count.
- There are multiple ways to iterate over a list in Python. Let’s see all the various ways to iterate over a list in Python, and performance comparison between them.
Method #1: Using For loop
[pastacode lang=”python” manual=”%23%20Python3%20code%20to%20iterate%20over%20a%20list%0AList%20%3D%20%5B1%2C%203%2C%205%2C%207%2C%209%5D%0A%20%20%0A%23%20Using%20for%20loop%0AFor%20i%20in%20list%3A%0A%20%20%20%20Print(i)%0A” message=”” highlight=”” provider=”manual”/]
Output
[pastacode lang=”bash” manual=”1%0A3%0A5%0A7%0A9%0A” message=”” highlight=”” provider=”manual”/]
Method #2: For loop and range ()
In case we would like to use the traditional for loop which iterates from number x to number y.
[pastacode lang=”python” manual=”%23%20Python3%20code%20to%20iterate%20over%20a%20list%0AList%20%3D%20%5B1%2C%203%2C%205%2C%207%2C%209%5D%0A%20%20%0A%23%20getting%20length%20of%20list%0ALength%20%3D%20len(list)%0A%20%20%0A%23%20Iterating%20the%20index%0A%23%20same%20as%20’for%20i%20in%20range(len(list))’%0AFor%20i%20in%20range(length)%3A%0A%20%20%20%20Print(list%5Bi%5D)%0A” message=”” highlight=”” provider=”manual”/]
Output
[pastacode lang=”bash” manual=”1%0A3%0A5%0A7%0A9%0A” message=”” highlight=”” provider=”manual”/]
Iterating using the index isn’t recommended if we will iterate over the elements (as done in Method #1).
Method #3: Using while loop
[pastacode lang=”python” manual=”%23%20Python3%20code%20to%20iterate%20over%20a%20list%0AList%20%3D%20%5B1%2C%203%2C%205%2C%207%2C%209%5D%0A%20%20%0A%23%20Getting%20length%20of%20list%0ALength%20%3D%20len(list)%0AI%20%3D%200%0A%20%20%0A%23%20Iterating%20using%20while%20loop%0AWhile%20i%20%3C%20length%3A%0A%20%20%20%20Print(list%5Bi%5D)%0A%20%20%20%20I%20%2B%3D%201%0A” message=”” highlight=”” provider=”manual”/]
Output
[pastacode lang=”bash” manual=”1%0A3%0A5%0A7%0A9%0A” message=”” highlight=”” provider=”manual”/]
Method #4: Using list comprehension (Possibly the most concrete way).
[pastacode lang=”python” manual=”%23%20Python3%20code%20to%20iterate%20over%20a%20list%0AList%20%3D%20%5B1%2C%203%2C%205%2C%207%2C%209%5D%0A%20%20%0A%23%20Using%20list%20comprehension%0A%5Bprint(i)%20for%20i%20in%20list%5D%0A” message=”” highlight=”” provider=”manual”/]
Output
[pastacode lang=”bash” manual=”1%0A3%0A5%0A7%0A9%0A” message=”” highlight=”” provider=”manual”/]
Method #5: Using enumerate ()
If we would like to convert the list into an iterable list of tuples (or get the index supported a condition check, for example in linear search you would possibly need to save the index of minimum element), you’ll use the enumerate() function.
[pastacode lang=”python” manual=”%23%20Python3%20code%20to%20iterate%20over%20a%20list%0AList%20%3D%20%5B1%2C%203%2C%205%2C%207%2C%209%5D%0A%20%20%0A%23%20Using%20enumerate()%20%0AFor%20i%2C%20val%20in%20enumerate(list)%3A%0A%20%20%20%20Print%20(i%2C%20%22%2C%22%2Cval)%0A” message=”” highlight=”” provider=”manual”/]
Output
[pastacode lang=”bash” manual=”0%2C%201%0A1%2C%203%0A2%2C%205%0A3%2C%207%0A4%2C%209%0A” message=”” highlight=”” provider=”manual”/]
Note: Even method #2 is used to find the index, but method #1 can’t (Unless an additional variable is incremented every iteration) and method #5 gives a concise representation of this indexing.
