python lists, lists in python, python

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Lists is a sequence and a basic data structure. A list may contain strings (text) and numbers. A list is similar to an array in other programming languages, but has additional functionality.

Python List

We define lists with brackets []. To access the data, these same brackets are used.
Example list usage:

#!/usr/bin/python

l = [ "Drake", "Derp", "Derek", "Dominique" ]

print(l)     # prints all elements
print(l[0])  # print first element
print(l[1])  # prints second element

Add/remove

We can use the functions append() and remove() to manipulate the list.

#!/usr/bin/python

l = [ "Drake", "Derp", "Derek", "Dominique" ]

print(l)                # prints all elements
l.append("Victoria")   # add element.
print(l)                # print all elements
l.remove("Derp")       # remove element.
l.remove("Drake")      # remove element.
print(l)               # print all elements.

Sort list

We can sort the list using the sort() function.

#!/usr/bin/python

l = [ "Drake", "Derp", "Derek", "Dominique" ]

print(l)     # prints all elements
l.sort()    # sorts the list in alphabetical order
print(l)     # prints all elements

If you want to have the list in descending order, simply use the reverse() function.

#!/usr/bin/python

l = [ "Drake", "Derp", "Derek", "Dominique" ]

print(l)     # prints all elements
l.sort()    # sorts the list in alphabetical order
l.reverse() # reverse order.
print(l)     # prints all elements

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Posted in beginner

2016-08-23

Leave a Reply:

Hattem • Mon, 08 Jun 2015

wow this is interest

Psk • Sat, 18 Jul 2015

Can ya make a 2D and 3D array too?

Frank • Sat, 18 Jul 2015

Yes, there is no limit to the number of dimensions in an array.

a 2d array:

#!/usr/bin/env python3

list = [[0, 1], [1, 2], [2, 3]]

print(list)
print(list[0][0])
print(list[1][1])

a 3d array:

#!/usr/bin/env python3

list = []

for i in xrange(3):
    list.append([])
    for j in xrange(3):
        list[i].append(i+j)

print(list)
print(list[0][0])
print(list[1][2])

Bheesam Jangra • Sat, 18 Jul 2015

when i am trying for this 3D array i am getting below error:

Traceback (most recent call last):
  File "hello.py", line 3, in 
    for i in xrange(3):
NameError: name 'xrange' is not defined

i have python35-32 installed on my PC and when i am trying to run this i am getting above error.

Frank • Sat, 18 Jul 2015

Try changing to:

#!/usr/bin/env python3

list = []

for i in range(3):
    list.append([])
    for j in range(3):
        list[i].append(i+j)

print(list)
print(list[0][0])
print(list[1][2])

Also try:

#!/usr/bin/env python3

list = [[0, 1, 2], [1, 2, 3], [2, 3, 4]]

print(list)
print(list[0][0])
print(list[1][1])

Abhishek • Tue, 11 Aug 2015

what is difference between list = [[0, 1], [1, 2], [2, 3]] and list = ([0, 1], [1, 2], [2, 3]) both appears to be array?

Staff • Tue, 11 Aug 2015

Good question! The second is a tuple, not a list. A tuple is a collection of variables that cannot be changed.
Once you try to set one of the tuple variables, you will get an exception. Try with this code:

#!/usr/bin/env python

setA = [[0, 1], [1, 2], [2, 3]]
setB = ([0, 1], [1, 2], [2, 3])

print(setA)
print(setB)

setA[0] = [2,3]
setB[0] = [2,3]

print(setA)
print(setB)

Jonas • Mon, 17 Aug 2015

When I type

l = [ "Drake", "Derp", "Derek", "Dominique" ]
and
print l

it gives an error:
SyntaxError: Missing parentheses in call to 'print'

Frank • Mon, 17 Aug 2015

Hi, you are using Python 3.x. Use: print(l)

Ben • Tue, 18 Aug 2015

a=['james','make','susan']
print a.reseve();

I expect the result is :['susan', 'make', 'james'] , but the it showed me like this :
>>> 
None
james
>>>

Did anyone can tell me why

Frank • Tue, 18 Aug 2015

Hi Ben, this will work:

>>> a=['james','make','susan']
>>> a.reverse()
>>> print a
['susan', 'make', 'james']

This is because reverse() returns None (see the function call paragraph). The function call changes its internal list but does not return the new list.
Some more examples:

>>> a=[1,2,3]
>>> print a.reverse()
None
>>> a
[3, 2, 1]

>>> a=['james','make','susan']
>>> print a.reverse()
None
>>> a
['susan', 'make', 'james']

Ben • Tue, 18 Aug 2015

Thank you so much . this function different from PHP/PERL

Nagendra • Fri, 21 Aug 2015

Hello ben,
a.reverse function will perform the reverse operation, it will store in the variable,
so call the variable then you got the answer ok
Regards,
Nagendra N

Blooper • Sat, 22 Aug 2015

I have a similar problem.
I defined the variable first as n.
When I command "print (n.sort())" or "print (n.reverse())" it responds "None" each time.

Frank • Sat, 22 Aug 2015

Call n.sort() or n.reverse() then print(n)

Ben • Thu, 27 Aug 2015

Hi,

a=[]

for i in range(1,10):
   if i%2 !=0:
      a.append[i]
print a[0]

But it showed : File "C:\Python27\learn\test.py", line 48, in
a.append[i]
TypeError: 'builtin_function_or_method' object has no attribute '__getitem__'?

why I can't via loops to append value to a list?

Frank • Thu, 27 Aug 2015

Hi Ben, use brackets for append. Like this:

#!/usr/bin/env python

a=[]

for i in range(1,10):
   if i%2 !=0:
      a.append(i)

print(a[0])
print(a)

Mike • Tue, 01 Sep 2015

hey having issues with this part

#!/usr/bin/python
l = [ "Drake", "Derp", "Derek", "Dominique" ]

print(l)     # prints all elements
print(l[0])  # print first element
print(l[1])  # prints second element
Output: 
on the print l[0]

im on python 3 i know nothing about this im just here trying to learn any help is apreciated

Frank • Tue, 01 Sep 2015

Hi Mike,

In Python 3.x the brackets are required:

#!/usr/bin/python3

l = [ "Drake", "Derp", "Derek", "Dominique" ]

print(l)     # prints all elements
print(l[0])  # print first element
print(l[1])  # prints second element

Mike • Tue, 01 Sep 2015


#!/usr/bin/python
l = [ "Drake", "Derp", "Derek", "Dominique" ]
print l     # prints all elements
print l[0]  # print first element
print l[1]  # prints second element

Output:
if when i try print l[0] and it doesnt work is it because im using python 3>?

Mike • Tue, 01 Sep 2015

thank you sir , if im a beginner and am going thru tutorials would you recommend i download the other version ?

Frank • Tue, 01 Sep 2015

Hi Mike,
If you use brackets you can use Python 3.x.
All of them should work

Frank • Wed, 02 Sep 2015

Yes. Use print(l[0]) for Python 3.x

Johnkw • Thu, 10 Sep 2015

i dont think its because of the python version..im using python 3 and its working very well even vat that part

Tinh Doan • Wed, 16 Sep 2015

when I run this code on "http://pythonspot.com/run.php" both of them is the same??
output is:

[[0, 1], [1, 2], [2, 3]]
([0, 1], [1, 2], [2, 3])

but when I run local, I get an error:
TypeError: 'tuple' object does not support item assignment

Tinh Doan • Wed, 16 Sep 2015

Why don't use:

list = [[0, 1, 4], [1, 2, 5], [2, 3, 6]]        
print(list)
print(list[0][0])
print(list[1][2])

Frank • Wed, 16 Sep 2015

The first one defines a list, the second one a tuple. Tuples cannot be given new values. You can read more on tuples here.

Frank • Wed, 16 Sep 2015

That should work too, only difference is first one is dynamic second static. It depends on your application

Lei • Tue, 24 Nov 2015

pyhton 2.7.10 is ok

José Chumán • Tue, 08 Dec 2015

Is there any way to print like this without using any loop? I'm using Python 3.x


l = [ "Drake", "Derp", "Derek", "Dominique" ]
Output:
Drake
Derp
Derek
Dominique

Frank • Tue, 08 Dec 2015

Loops are preferred but yes, you can print them one by one:

l = ["Drake","Derp","Derek","Dominique"]
print(l[0])
print(l[1])
print(l[2])
print(l[3])

There is another method, but loops would create the cleanest code.

Ayesha • Sat, 16 Jan 2016

How can i print the items in the list randomly

Frank • Sun, 24 Jan 2016

You can use the random.shuffle() method:

#!/usr/bin/python
import random

list = [ "Drake", "Derp", "Derek", "Dominique" ]
random.shuffle(list)
print(list)