Why I have IndexError when program makes succesful first step? - python

I tried to make sorter that deletes duplicates of IP's in first list and saves it into a file, but after first succesful round it gives me IndexError: list index out of range.
I've expected normal sorting process, but it doesn't works
Code:
ip1 = open('hosts', 'r')
ip2 = open('rotten', 'r')
ipList1 = [line.strip().split('\n') for line in ip1]
ipList2 = [line.strip().split('\n') for line in ip2]
for i in range(len(ipList1)):
for a in range(len(ipList2)):
if(ipList1[i] == ipList2[a]):
print('match')
del(ipList1[i])
del(ipList2[a])
i -= 1
a -= 1
c = open('end', 'w')
for d in range(len(ipList1)):
c.write(str(ipList1[d]) + '\n')
c.close()

You're deleting from the list while iterating over it, that's why you're getting an IndexError.
This could be easier done with sets:
with open('hosts') as ip1, open('rotten') as ip2:
ipList1 = set(line.strip().split('\n') for line in ip1)
ipList2 = set(line.strip().split('\n') for line in ip2)
good = ipList1 - ipList2
with open('end', 'w') as c:
for d in good:
c.write(d + '\n')

You changed lists in a fly. For expression gets a list with, as an example, of 5 elements length, after the first iteration you remove 4, so in the second iteration for tried to extract the second element but now it does not exist.
If necessary save the ordering you can use generator expression:
ips = [ip for ip in ipList1 if ip not in set(list2)]
If doesn't, just use sets expression.

You should never modify a list that you are currently iterating over.
A fix would be just to make a third list that saves the non duplicates. Another way would be to just use sets and subtract them from each other although I do know if you like duplicates in one list itself. Also, the way you are doing it right now a duplicate is only found if its at the same index.
ip2 = open('rotten', 'r')
ipList1 = [line.strip().replace('\n', '') for line in ip1]
ipList2 = [line.strip().replace('\n', '') for line in ip2]
ip1.close()
ip2.close()
newlist = []
for v in ip1:
if v not in ip2:
newlist.append(v)
c = open('end', 'w')
c.write('\n'.join(newlist))
c.close()

Other answers focus on deleting from a container while iterating over it. While that’s generally a bad idea, it’s not the crux of the problem here because you have (unpythonically) set up the for loops to use a sequence of indices, and so you aren’t strictly speaking iterating over the lists themselves anyway.
No, the problem here is that i-=1 and a-=1 have no effect: when a for loop begins a new iteration, it doesn’t work off of the previous value of the index. It just takes the next value that it was always destined to take, from the iterator that you established at the beginning (in your case, the output of range())

Related

How to assign a new value to the list in running loop

My data cutting loop seems to run ok in the loop, but when it prints the result outside the loop, the contents are unchanged. Presuming it's buggy because I'm trying to assign to what the for loop is running through, but I don't know.
For reference, it's a small web review scraper project I'm working on. To get it formatted to CSV with pandas I think all the data needs to end at the same point (length), so I'm cutting any lists that are longer than the shortest. The values "cust_stars_result, rev_result, cust_res" are all lists with basics strings stored inside, in this case equal to lengths 16, 12, and 15. I try to slice everything down to 12 in the end but the results are overwritten. What is the right/best way to go about this?
star_len = len(cust_stars_result)
rev_len = len(rev_result)
custname_len = len(cust_res)
print('customer name length: ' + str(custname_len) + ' -- review length: ' + str(rev_len) + ' -- star length: ' + str(star_len))
datalen = [star_len, rev_len, custname_len]
print(min(datalen))
datapack = [cust_stars_result, rev_result, cust_res]
# LOOPER FOR CULLING
for data in datapack:
if len(data) != min(datalen):
print("operating culler to make data even length")
print(len(data))
data = data[: min(datalen)]
print(len(data)) #this comes out OK
else:
print("equal length, skipping culler")
pass
print(datapack) # prints the original values
Inside your loop you update the data variable but that's just reassigning the value of that variable. You want to do something like
for i, data in enumerate(datapack):
...
datapack[i] = data[: min(datalen)]
This will update the datapack element
While "trying to assign to what the for loop is running through" is a real issue, in this case the problem is rather that your code is not assigning anything to datapack when you change data. Instead, what it does is assign each item in datapack to data, so when you change data, datapack remain unchanged.
Instead, try either adding each item to new list, and then assigning datapack to equal the new list:
temp = []
for data in datapack:
...
temp.append(data[:min(datalen)])
datapack = temp
Or try using a range or enumerate loop:
for i, data in enumerate(datapack):
...
datapack[i] = data[:min(datalen)]
There are more fancy ways (but less readable and debuggable) to accomplish what you're doing here (slicing off the end of the list), such as the below which uses list comprehension and map:
mindatalen = min(map(len, datapack))
datapack = [data[:mindatalen]for data in datapack]

Extracting multiple data from a single list

I working on a text file that contains multiple information. I converted it into a list in python and right now I'm trying to separate the different data into different lists. The data is presented as following:
CODE/ DESCRIPTION/ Unity/ Value1/ Value2/ Value3/ Value4 and then repeat, an example would be:
P03133 Auxiliar helper un 203.02 417.54 437.22 675.80
My approach to it until now has been:
Creating lists to storage each information:
codes = []
description = []
unity = []
cost = []
Through loops finding a code, based on the code's structure, and using the code's index as base to find the remaining values.
Finding a code's easy, it's a distinct type of information amongst the other data.
For the remaining values I made a loop to find the next value that is numeric after a code. That way I can delimitate the rest of the indexes:
The unity would be the code's index + index until isnumeric - 1, hence it's the first information prior to the first numeric value in each line.
The cost would be the code's index + index until isnumeric + 2, the third value is the only one I need to store.
The description is a little harder, the number of elements that compose it varies across the list. So I used slicing starting at code's index + 1 and ending at index until isnumeric - 2.
for i, carc in enumerate(txtl):
if carc[0] == "P" and carc[1].isnumeric():
codes.append(carc)
j = 0
while not txtl[i+j].isnumeric():
j = j + 1
description.append(" ".join(txtl[i+1:i+j-2]))
unity.append(txtl[i+j-1])
cost.append(txtl[i+j])
I'm facing some problems with this approach, although there will always be more elements to the list after a code I'm getting the error:
while not txtl[i+j].isnumeric():
txtl[i+j] list index out of range.
Accepting any solution to debug my code or even new solutions to problem.
OBS: I'm also going to have to do this to a really similar data font, but the code would be just a sequence of 7 numbers, thus harder to find amongst the other data. Any solution that includes this facet is also appreciated!
A slight addition to your code should resolve this:
while i+j < len(txtl) and not txtl[i+j].isnumeric():
j += 1
The first condition fails when out of bounds, so the second one doesn't get checked.
Also, please use a list of dict items instead of 4 different lists, fe:
thelist = []
thelist.append({'codes': 69, 'description': 'random text', 'unity': 'whatever', 'cost': 'your life'})
In this way you always have the correct values together in the list, and you don't need to keep track of where you are with indexes or other black magic...
EDIT after comment interactions:
Ok, so in this case you split the line you are processing on the space character, and then process the words in the line.
from pprint import pprint # just for pretty printing
textl = 'P03133 Auxiliar helper un 203.02 417.54 437.22 675.80'
the_list = []
def handle_line(textl: str):
description = ''
unity = None
values = []
for word in textl.split()[1:]:
# it splits on space characters by default
# you can ignore the first item in the list, as this will always be the code
# str.isnumeric() doesn't work with floats, only integers. See https://stackoverflow.com/a/23639915/9267296
if not word.replace(',', '').replace('.', '').isnumeric():
if len(description) == 0:
description = word
else:
description = f'{description} {word}' # I like f-strings
elif not unity:
# if unity is still None, that means it has not been set yet
unity = word
else:
values.append(word)
return {'code': textl.split()[0], 'description': description, 'unity': unity, 'values': values}
the_list.append(handle_line(textl))
pprint(the_list)
str.isnumeric() doesn't work with floats, only integers. See https://stackoverflow.com/a/23639915/9267296

Python readlines() doesn't function outputs bug in for loop

Intro:
I'm a beginner python learning syntax at the moment. I've come across this concept of reading and writing files natively supported by python. I've figured to give it a try and find bugs after attempting looping reading and writing commands. I wanted to randomly pick a name from a name file and then writing it into a new file. My file includes 19239 lines of names, randrange(18238) generates from 0 - 18238, and, supposedly, would read a randomly read a line between 1 - 18239. The problem is that the code that reads and writes works without the for loop but not with the for loop.
My attempt:
from random import randrange
rdname = open("names.dat", "r")
wrmain = open("main.dat", "a")
rdmain = open("main.dat", "r")
for x in range(6):
nm = rdname.readlines()[randrange(18238)]
print(str(randrange(18238)) + ": " + nm)
wrmain.write("\n" + nm)
...
Error code:
Exception has occurred: IndexError
list index out of range
Good luck with your programming journey.
The readlines() method. Has some non-intuitive behaviour. When you use the readlines() it "dumps" the entire content of the file and returns a list of strings of each line. Thus the second time you call the rdname.readlines()[randrange(18238)], the rdname file object is completely empty and you actually have an empty list. So functionally you are telling your programme to run [][randrange(18238)] on the second iteration of the loop.
I also took the liberty of fixing the random number call, as the way you had implemented it would mean it would call 2 different random numbers when selecting the name nm = rdname.readlines()[randrange(18238)] and printing the selected name and linenumber print(str(randrange(18238)) + ": " + nm)
...
rdname = open("names.dat", "r")
wrmain = open("main.dat", "a")
rdmain = open("main.dat", "r")
rdname_list = rdname.readlines()
for x in range(6):
rd_number = randrange(18238)
nm = rdname_list[rd_number]
print(str(rd_number) + ": " + nm)
wrmain.write("\n" + nm)
...
rdname.readlines() exhausts your file handle. Running rdname.readlines() gives you the list of lines the first time, but returns an empty list every subsequent time. Obviously, you can't access an element in an empty list. To fix this, assign the result of readlines() to a variable just once, before your loop.
rdlines = rdname.readlines()
maxval = len(rdlines)
for x in range(6):
randval = randrange(maxval)
nm = rdlines[randval]
print(str(randval) + ": " + nm)
wrmain.write("\n" + nm)
Also, making sure your random number can only go to the length of your list is a good idea. No need to hardcode the length of the list though -- the len() function will give you that.
I highly recommend you take a look at how to debug small programs. Using a debugger to step through your code is immensely helpful because you can see how each line affects the values of your variables. In this case, if you'd looked at the value of nm in each iteration, it would be obvious why you got the IndexError, and finding out that nm becomes an empty list on readlines() would point you in the direction of the answer.

Assign variable if list index out of range python error

How to pass a string to a variable if an index error is found? Consider the code:
for l1, l2 in zip(open('file1.list'), open ('file2.list')):
a=fasta1[int(l1)]
b=fasta2[int(l2)]
alignments = pairwise2.align.globalxx(a,b)
top_aln = alignments[0]
aln_a, aln_b, score, begin, end = top_aln
print aln_a+'\n'+aln_b
outfast1 = aln_a
outfast2 = aln_b
A number of these functions must be imported (pairwise2 align),
but the file.lists are single column text files with one sequence id (text and numbers) per line, that are used to extract from the fasta1 and fasta2 text files.
Basically, I want to try: each list command ( a=fasta1[int(l1)]) and if there is no error (the id is in range), do as normal (assign variables a and b for that iteration), but if NOT, assign the 'a' variable some placeholder text like 'GGG':
for l1, l2 in zip(open('file1.list'), open ('file2.list')):
try:
a=fasta1[int(l1)]
except IndexError,e:
a="GGG"
continue
try:
b=fasta2[int(l2)]
except (IndexError):
b="CCC"
continue
This code doesn't quite work (when integrated with above code), which isn't surprising given my lack of python prowess, but I don't quite know why. I actually get no text output, despite the print calls... Am I thinking about this right? If there is NO error in the index, I just want it to go on and do the pairwise alignment (with the first a and b variables) and then print some text to stdout.
Any ideas?
Python's conditional (aka ternary) expressions can one-line this for you. They're often criticized for lack of readability, but I think this example reads well enough.
a = fasta1[int(l1)] if int(l1) < len(fasta1) else "GGG"
You don't need continue, because it will skip that iteration of the loop. Consider the following:
for l1, l2 in zip(open('file1.list'), open ('file2.list')):
a = 'GGG'
b = 'CCC'
try:
a = fasta1[int(l1)]
b = fasta2[int(l2)]
except IndexError:
pass

Python, I need the following code to finish quicker

I need the following code to finish quicker without threads or multiprocessing. If anyone knows of any tricks that would be greatly appreciated. maybe for i in enumerate() or changing the list to a string before calculating, I'm not sure.
For the example below, I have attempted to recreate the variables using a random sequence, however this has rendered some of the conditions inside the loop useless ... which is ok for this example, it just means the 'true' application for the code will take slightly longer.
Currently on my i7, the example below (which will mostly bypass some of its conditions) completes in 1 second, I would like to get this down as much as possible.
import random
import time
import collections
import cProfile
def random_string(length=7):
"""Return a random string of given length"""
return "".join([chr(random.randint(65, 90)) for i in range(length)])
LIST_LEN = 18400
original = [[random_string() for i in range(LIST_LEN)] for j in range(6)]
LIST_LEN = 5
SufxList = [random_string() for i in range(LIST_LEN)]
LIST_LEN = 28
TerminateHook = [random_string() for i in range(LIST_LEN)]
#^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Exclude above from benchmark
ListVar = original[:]
for b in range(len(ListVar)):
for c in range(len(ListVar[b])):
#If its an int ... remove
try:
int(ListVar[b][c].replace(' ', ''))
ListVar[b][c] = ''
except: pass
#if any second sufxList delete
for d in range(len(SufxList)):
if ListVar[b][c].find(SufxList[d]) != -1: ListVar[b][c] = ''
for d in range(len(TerminateHook)):
if ListVar[b][c].find(TerminateHook[d]) != -1: ListVar[b][c] = ''
#remove all '' from list
while '' in ListVar[b]: ListVar[b].remove('')
print(ListVar[b])
ListVar = original[:]
That makes a shallow copy of ListVar, so your changes to the second level lists are going to affect the original also. Are you sure that is what you want? Much better would be to build the new modified list from scratch.
for b in range(len(ListVar)):
for c in range(len(ListVar[b])):
Yuck: whenever possible iterate directly over lists.
#If its an int ... remove
try:
int(ListVar[b][c].replace(' ', ''))
ListVar[b][c] = ''
except: pass
You want to ignore spaces in the middle of numbers? That doesn't sound right. If the numbers can be negative you may want to use the try..except but if they are only positive just use .isdigit().
#if any second sufxList delete
for d in range(len(SufxList)):
if ListVar[b][c].find(SufxList[d]) != -1: ListVar[b][c] = ''
Is that just bad naming? SufxList implies you are looking for suffixes, if so just use .endswith() (and note that you can pass a tuple in to avoid the loop). If you really do want to find the the suffix is anywhere in the string use the in operator.
for d in range(len(TerminateHook)):
if ListVar[b][c].find(TerminateHook[d]) != -1: ListVar[b][c] = ''
Again use the in operator. Also any() is useful here.
#remove all '' from list
while '' in ListVar[b]: ListVar[b].remove('')
and that while is O(n^2) i.e. it will be slow. You could use a list comprehension instead to strip out the blanks, but better just to build clean lists to begin with.
print(ListVar[b])
I think maybe your indentation was wrong on that print.
Putting these suggestions together gives something like:
suffixes = tuple(SufxList)
newListVar = []
for row in original:
newRow = []
newListVar.append(newRow)
for value in row:
if (not value.isdigit() and
not value.endswith(suffixes) and
not any(th in value for th in TerminateHook)):
newRow.append(value)
print(newRow)

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