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Python 3 Error Missunderstanding (IndexError)

Here's my code
def abc(l,z):
L=[]
länge= len(L)
for x in range(0, länge+1):
L[x]+z
print(L)
abc(["1","2","3"],"-")
I want the program to output "1-2-3"
l in abc(l,z) should be a List out of Strings which combines "l" and "z" to a single String.
I'm getting an Index Error: list index out of range.

There are a couple of issues here.
First, range(0, länge+1) will stop at länge but your list only has indexes from 0 tolänge - 1, so that's one source for an IndexError.
Second, L[x]+z will give you another IndexError because L is empty but you try to access L[0] (and in the next iteration, where you don't get because of the error, L[1], L[2], and so on).
Third, even without an IndexError the statement L[x]+z will do nothing. You compute the value of L[x]+z but then you don't assign any variable to it, so it is immediately lost.
Fourth, in order to print your final result, put the call to print after the for loop, not inside. Consider using return instead of print if you actually want to do something with the result the function produces (make sure to educate yourself on the difference between print and return).
Fifth, you want to build a string, so the usage of the list L does not make much sense. Start with an empty string and add the current item from l and z to it in the loop body (coupled with a re-assignment in order to not lose the freshly computed value).
Lastly, there's no point in using range here. You can iterate over values in a list direclty by simply writing for x in l:.
That should give you enough to work with and fix your code for now.
(If you don't care why your function does not work and this is not an exercise, simply use str.join as suggested in the comments.)

The TypeError in python

I'm trying to make a challenge for one of the courses I'm following. I'm new to programming, but I'm eager to learn.
Can you tell me in detail why this error occurs to me and how do solve it.
default_names =['Justin', 'john','Emilee', 'jim','Ron','Sandra','veronica','Wiskley']
i=0
for i in default_names:
default_names[i]=default_names[i][0].upper()
i+=1
if i==len(default_names):
break
print default_names
the error: TypeError: list indices must be integers, not str

default_names =['Justin', 'john','Emilee', 'jim','Ron','Sandra','veronica','Wiskley']
for i in range(len(default_names)):
default_names[i]=default_names[i].upper()
print default_names

What you are looking for is :
for i,s in enumerate(default_names):
or simple:
for i in range(len(default_names)):
The mistake you are doing is that when you say for i in default_names: notice that i value is a string, not int as you are trying to use.
for i in default_names:
print(i)
Will give :
OUT: Justin
john
Emilee
jim
Ron
Sandra
veronica
Wiskley
So the actual code should be, assuming you are trying to convert each string in list to Upper case :
for i in range(len(default_names)):
default_names[i]=default_names[i].upper()
EDIT : The OP wants only First char to be Upper case, and since string are immutable, change of code to :
for i in range(len(default_names)):
default_names[i]=default_names[i][0].upper() + default_names[i][1:]

As you can see in your error: TypeError: list indices must be integers, not str. It's because to access the elements of a list, you have to use the index, which is an integer. Basing on the structure of your code, you might have come from a different language. Python's for loop is different from the other languages. It doesn't increment the variable you made over the loop, but rather it iterates over the elements and passes the value to the variable. I think it would be more suitable to use a while loop with the code you made since you have initialized your i to 0. E.g.
default_names =['Justin', 'john','Emilee', 'jim','Ron','Sandra','veronica','Wiskley']
i=0
while i < len(default_names):
default_names[i]=default_names[i].upper() #removed the [0] here
i+=1
#removed the other codes here
print default_names
As you become better in python, you can find more efficient ways to do these kinds of things. The result you wanted could be simply made through
default_names = [name.upper() for name in default_names]
which simply iterates all of the names, makes it upper case and saves it back to default_names

How to join multiple rows into single line using python? [duplicate]

I am trying to append objects to the end of a list repeatedly, like so:
list1 = []
n = 3
for i in range(0, n):
list1 = list1.append([i])
But I get an error like: AttributeError: 'NoneType' object has no attribute 'append'. Is this because list1 starts off as an empty list? How do I fix this error?
This question is specifically about how to fix the problem and append to the list correctly. In the original code, the reported error occurs when using a loop because .append returns None the first time. For why None is returned (the underlying design decision), see Why do these list operations return None, rather than the resulting list?.
If you have an IndexError from trying to assign to an index just past the end of a list - that doesn't work; you need the .append method instead. For more information, see Why does this iterative list-growing code give IndexError: list assignment index out of range? How can I repeatedly add elements to a list?.
If you want to append the same value multiple times, see Python: Append item to list N times.

append actually changes the list. Also, it takes an item, not a list. Hence, all you need is
for i in range(n):
list1.append(i)
(By the way, note that you can use range(n), in this case.)
I assume your actual use is more complicated, but you may be able to use a list comprehension, which is more pythonic for this:
list1 = [i for i in range(n)]
Or, in this case, in Python 2.x range(n) in fact creates the list that you want already, although in Python 3.x, you need list(range(n)).

You don't need the assignment operator. append returns None.

append returns None, so at the second iteration you are calling method append of NoneType. Just remove the assignment:
for i in range(0, n):
list1.append([i])

Mikola has the right answer but a little more explanation. It will run the first time, but because append returns None, after the first iteration of the for loop, your assignment will cause list1 to equal None and therefore the error is thrown on the second iteration.

I personally prefer the + operator than append:
for i in range(0, n):
list1 += [[i]]
But this is creating a new list every time, so might not be the best if performance is critical.

Note that you also can use insert in order to put number into the required position within list:
initList = [1,2,3,4,5]
initList.insert(2, 10) # insert(pos, val) => initList = [1,2,10,3,4,5]
And also note that in python you can always get a list length using method len()

Like Mikola said, append() returns a void, so every iteration you're setting list1 to a nonetype because append is returning a nonetype. On the next iteration, list1 is null so you're trying to call the append method of a null. Nulls don't have methods, hence your error.

use my_list.append(...)
and do not use and other list to append as list are mutable.

Python KeyError: 0 when working with dictionary and functions

I'm new to Python so my question may seem easy to some but then again I'm stuck on my own so I need your help! This is the code that i am having trouble with:
def identify_language(sequence, **common_words):
result = {}
for i in common_words:
result[i] = 0
for i in func_op(sequence.lower()):
for j in common_words:
if i in common_words[j]:
result[j] += 1
return sort(result[0][0])
...
dictionary = {'cro':list_cro, 'eng':list_cro}
language = identify_language('I had a little lamb. It was called Billy.', **dictionary)
I am trying to identify language based on samples which are in list_cro and list_eng (and hopefully others). I am getting KeyError: 0. Additionally, sort and func_op are working fine i tested then separately. What may be the problem?
Also, if i change order of arguments in function (putting list as a first argument and string as second) i am getting syntax error.
Thanks for listening!

At the end of the function, result should look like this: {'cro': X, 'eng': Y}, where X and Y are numbers. I don't know what your dictionaries are, so I can't guess what the numbers are. Evaluating result['eng'] will produce a number, as will result['cro'], but there is no 0 key in this dictionary.
Further, the second indexing operation will also give you issues. result['eng'][0] will give you an error because result['eng'] is a number, and you can't index into a number.
What do you expect the output of this function to look like? Where is sort defined and what is it supposed to do?

Introductory Python task from the edX MIT class

I have recently started learning Python in the MIT class on edX.
However, I have been having some trouble with certain exercises. Here is one of them:
"Write a procedure called oddTuples, which takes a tuple as input, and returns a new tuple as output, where every other element of the input tuple is copied, starting with the first one. So if test is the tuple ('I', 'am', 'a', 'test', 'tuple'), then evaluating oddTuples on this input would return the tuple ('I', 'a', 'tuple'). "
The correct code, according to the lecture, is the following:
def oddTuples(aTup):
'''
aTup: a tuple
returns: tuple, every other element of aTup.
'''
# a placeholder to gather our response
rTup = ()
index = 0
# Idea: Iterate over the elements in aTup, counting by 2
# (every other element) and adding that element to
# the result
while index < len(aTup):
rTup += (aTup[index],)
index += 2
return rTup
However, I have tried to solve it myself in a different way with the following code:
def oddTuples(aTup):
'''
aTup: a tuple
returns: tuple, every other element of aTup.
'''
# Your Code Here
bTup=()
i=0
for i in (0,len(aTup)-1):
if i%2==0:
bTup=bTup+(aTup[i],)
print(bTup)
print(i)
i+=1
return bTup
However, my solution does not work and I am unable to understand why (I think it should do essentially the same thing as the code the tutors provide).

I just like to add that the pythonic solution for this problem uses slices with a stepwidth and is:
newTuple = oldTuple[::2]
oldTuple[::2] has the meaning: Get copy of oldtuple from start (value is omitted) to end (omitted) with a spepwidth of 2.

I think I get the problem here.
In your for loop you specify two fixed values for i:
0
len(aTup)-1
Want you really want is the range of values from 0 to len(aTup)-1:
0
1
2
...
len(aTup)-1
In order to convert start and end values into all values in a range you need to use Python's range method:
for i in range(0,len(aTup)-1):
(Actually if you take a look into range's documentation, you will find out there is a third parameter called skip. If you use it your function becomes kind of irrelevant :))

Your code should read:
for i in range(0,len(aTup)):
# i=0, 1, 2 ..., len(aTup)-1.
rather than
for i in (0,len(aTup)-1):
# i=0 or i=len(aTup)-1.

The lines for i in (0,len(aTup)-1): and i+=1 aren't quite doing what you want. As in other answers, you probably want for i in range(0,len(aTup)-1): (insert range), but you also want to remove i+=1, since the for-in construct sets the value of i to each of the items in the iterable in turn.

Okay when running your code the output is the following:
('I', 'tuple')
This is because the problem in the code you wrote is the way you implement the for loop.
Instead of using:
for i in (0,len(aTup)-1):
You should change that to the following and your code will work:
for i in range(len(aTup)):
the range function basically creates a list of integers ranging from 0 to the length of your tuple - 1.
So your code should after editing it should look like:
def oddTuples(aTup):
bTup=()
for i in range(len(aTup)):
if i%2==0:
bTup=bTup+(aTup[i],)
return bTup