Creating for loop until list.length

Question

I’m reading about for loops right now, and I am curious if it’s possible to do a for loop in Python like in Java.

Is it even possible to do something like

for (int i = 1; i < list.length; i++)

and can you do another for loop inside this for loop ?

Thanks

Asked By: Agape

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Source

Answer 1

You could learn about Python loops here:
http://en.wikibooks.org/wiki/Python_Programming/Loops

You have to know that Python doesn’t have { and } for start and end of loop, instead it depends on tab chars you enter in first of line, I mean line indents.

So you can do loop inside loop with double tab (indent)

An example of double loop is like this:

onetoten = range(1,11)
tentotwenty = range(10,21)
for count in onetoten:
    for count2 in tentotwenty
        print(count2)

Answered By: Vahid Farahmand

Answer 2

Yes you can, with range ^[docs]:

for i in range(1, len(l)):
    # i is an integer, you can access the list element with l[i]

but if you are accessing the list elements anyway, it’s more natural to iterate over them directly:

for element in l:
   # element refers to the element in the list, i.e. it is the same as l[i]

If you want to skip the the first element, you can slice the list ^[tutorial]:

for element in l[1:]:
    # ...

can you do another for loop inside this for loop

Sure you can.

Answered By: Felix Kling

Answer 3

In Python you can iterate over the list itself:

for item in my_list:
   #do something with item

or to use indices you can use xrange():

for i in xrange(1,len(my_list)):    #as indexes start at zero so you 
                                    #may have to use xrange(len(my_list))
    #do something here my_list[i]

There’s another built-in function called enumerate(), which returns both item and index:

for index,item in enumerate(my_list):
    # do something here

examples:

In [117]: my_lis=list('foobar')

In [118]: my_lis
Out[118]: ['f', 'o', 'o', 'b', 'a', 'r']

In [119]: for item in my_lis:
    print item
   .....:     
f
o
o
b
a
r

In [120]: for i in xrange(len(my_lis)):
    print my_lis[i]
   .....:     
f
o
o
b
a
r

In [122]: for index,item in enumerate(my_lis):
    print index,'-->',item
   .....:     
0 --> f
1 --> o
2 --> o
3 --> b
4 --> a
5 --> r

Answered By: Ashwini Chaudhary

Answer 4

The answer depends on what do you need a loop for.

of course you can have a loop similar to Java:

for i in xrange(len(my_list)):

but I never actually used loops like this,

because usually you want to iterate

for obj in my_list

or if you need an index as well

for index, obj in enumerate(my_list)

or you want to produce another collection from a list

map(some_func, my_list)

[somefunc[x] for x in my_list]

also there are itertools module that covers most of iteration related cases

also please take a look at the builtins like any, max, min, all, enumerate

I would say – do not try to write Java-like code in python. There is always a pythonic way to do it.

Answered By: RomanI

Creating for loop until list.length

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