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Adding a new string to the end of a specific line in a text file

I'm new to python hence I am unable to implement the solutions I've found online in order to fix my problem.
I am trying to add a specific string to the end of a specific line to a textfile. As I understand text commands, I must overwrite the file if I don't want to append to the end of it. So, my solution is as follows:
ans = 'test'
numdef = ['H',2]
f = open(textfile, 'r')
lines = f.readlines()
f.close()
f = open(textfile, 'w')
f.write('')
f.close()
f = open(textfile, 'a')
for line in lines:
if int(line[0]) == numdef[1]:
if str(line[2]) == numdef[0]:
k = ans+ line
f.write(k)
else:
f.write(line)
Basically, I am trying to add variable ans to the end of a specific line, the line which appears in my list numdef. So, for example, for
2 H: 4,0 : Where to search for information : google
I want
2 H: 4,0 : Where to search for information : google test
I have also tried using line.insert() but to no avail.
I understand using the 'a' function of the open command is not so relevant and helpful here, but I am out of ideas. Would love tips with this code, or if maybe I should scrap it and rethink the whole thing.
Thank you for your time and advice!

When you use the method
lines = f.readlines()
Python automatically adds "\n" to the end of each line.
Try instead of :
k = line+ans
The following:
k = line.rstrip('\n') + ans
Good luck!

Try this. You don't have an else case if it meets the first requirement but not the other.
ans = 'test'
numdef = ['H',2]
f = open(textfile, 'r')
lines = f.readlines()
f.close()
f = open(textfile, 'w')
f.write('')
f.close()
f = open(textfile, 'a')
for line in lines:
if int(line[0]) == numdef[1] and str(line[2]) == numdef[0]:
k = line.replace('\n','')+ans
f.write(k)
else:
f.write(line)
f.close()
Better way:
#initialize variables
ans = 'test'
numdef = ['H',2]
#open file in read mode, add lines into lines
with open(textfile, 'r') as f:
lines=f.readlines()
#open file in write mode, override everything
with open(textfile, 'w') as f:
#in the list comprehension, loop through each line in lines, if both of the conditions are true, then take the line, remove all newlines, and add ans. Otherwise, remove all the newlines and don't add anything. Then combine the list into a string with newlines as separators ('\n'.join), and write this string to the file.
f.write('\n'.join([line.replace('\n','')+ans if int(line[0]) == numdef[1] and str(line[2]) == numdef[0] else line.replace('\n','') for line in lines]))

Changing a text file and making a bigger text file in python

I have a tab separated text file like these example:
infile:
chr1 + 1071396 1271396 LOC
chr12 + 1101483 1121483 MIR200B
I want to divide the difference between columns 3 and 4 in infile into 100 and make 100 rows per row in infile and make a new file named newfile
and make the final tab separated file with 6 columns. The first 5 columns would be like infile, the 6th column would be (5th column)_part number (number is 1 to 100).
This is the expected output file:
expected output:
chr1 + 1071396 1073396 LOC LOC_part1
chr1 + 1073396 1075396 LOC LOC_part2
.
.
.
chr1 + 1269396 1271396 LOC LOC_part100
chr12 + 1101483 1101683 MIR200B MIR200B_part1
chr12 + 1101683 1101883 MIR200B MIR200B_part2
.
.
.
chr12 + 1121283 1121483 MIR200B MIR200B_part100
I wrote the following code to get the expected output but it does not return what I expect.
file = open('infile.txt', 'rb')
cont = []
for line in file:
cont.append(line)
newfile = []
for i in cont:
percent = (i[3]-i[2])/100
for j in percent:
newfile.append(i[0], i[1], i[2], i[2]+percent, i[4], i[4]_'part'percent[j])
with open('output.txt', 'w') as f:
for i in newfile:
for j in i:
f.write(i + '\n')
Do you know how to fix the problem?

Try this:
file = open('infile.txt', 'rb')
cont = []
for line in file:
cont.append(list(filter(lambda x: not x.isspace(), line.split(' ')))
newfile = []
for i in cont:
diff= (int(i[3])-int(i[2]))/100
left = i[2]
right = i[2] + diff
for j in range(100):
newfile.append(i[0], i[1], left, right, i[4], i[4]_'part' + j)
left = right
right = right + diff
with open('output.txt', 'w') as f:
for i in newfile:
for j in i:
f.write(i + '\n')
In your code for i in cont youre loop over the string and i is a char and not string.
To fix that i split the line and remove spaces.

Here are some suggestions:
when you open the file, open it as a text file, not a binary file.
open('infile.txt','r')
now, when you read it line by line, you should strip the newline character at the end by using strip(). Then, you need to split your input text line by tabs into a list of strings, vs a just a long string containing your line, by using split('\t'):
line.strip().split('\t')
now you have:
file = open('infile.txt', 'r')
cont = []
for line in file:
cont.append(line.strip().split('\t))
now cont is a list of lists, where each list contains your tab separated data. i.e.
cont[1][0] = 'chr12'.
You will probably able to take it from here.

Others have answered your question with respect to your own code, I thought I would leave my attempt at solving your problem here.
import os
directory = "C:/Users/DELL/Desktop/"
filename = "infile.txt"
path = os.path.join(directory, filename)
with open(path, "r") as f_in, open(directory+"outfile.txt", "w") as f_out: #open input and output files
for line in f_in:
contents = line.rstrip().split("\t") #split line into words stored as a string 'contents'
diff = (int(contents[3]) - int(contents[2]))/100
for i in range(100):
temp = (f"{contents[0]}\t+\t{int(int(contents[2])+ diff*i)}\t{contents[3]}\t{contents[4]}\t{contents[4]}_part{i+1}")
f_out.write(temp+"\n")
This code doesn't follow python style convention well (excessively long lines, for example) but it works. The line temp = ... uses fstrings to format the output string conveniently, which you could read more about here.

write result of for statement

I'm very new to Python, and attempt to do the following
read file,
replace spaces with new lines,
remove any line containing the ":" character
write result to text file
So far I have got the following, I know there should be a o.write somewhere, however I've tried a bunch of different spots and nothing seems to work, I'm pretty sure I'm missing something simple.
import os
i = open("input.txt", "r+")
o = open("output.txt", "a+")
for line in i.readlines():
(line.replace(" ", "\n"))
if ":" in line:
(line)
i.close()
o.close()
The input file is as follows
192.168.1.1 192.168.2.1 192.168.3.1 2001:0db8:85a3:0000:0000:8a2e:0370:7334

So I have:
EDITED to remove lines with a :
test.txt
192.168.1.1 192.168.2.1 192.168.3.1 2001:0db8:85a3:0000:0000:8a2e:0370:7334
answer.py
with open('test.txt', 'r') as f:
text = f.read()
lines = text.split(' ')
lines = [line for line in lines if ':' not in line]
with open('result.txt', 'w') as f:
f.write('\n'.join(lines))
result.txt
192.168.1.1
192.168.2.1
192.168.3.1
Is that what you wanted?

you can build your new file contents first and afterward write to it:
import os
i = open("in", "r+")
o = open("out", "a+")
result = ""
for line in i.readlines():
if ":" not in line:
result += line.replace(" ", "\n")
o.write(result)
i.close()
o.close()

Replaces the spaces with newlines before iterating over the file's contents. if you don't, then you'll only be iterating over a single line.
There's no need for the os library in your code.
Call o.write(line) after testing if the line has no colon(:).
Use the context manger to do your I/O operations.
Use more descriptive names than i and o to avoid writing confusing code.
With the above modifications, your code becomes:
with open("input.txt", "r+") as infile, open("output.txt", "a+") as outfile:
contents = infile.read().replace(' ', '\n')
for line in contents.split('\n'):
if ':' not in line:
outfile.write(line + '\n')

Counting to 100,000 and writing that to a file

I haven't used Python for a while but I decided to create a program today to help me with some work I am trying to do. I am trying to create a program that writes the numbers 1-100,000 with the symbol | after each but can't seem to strip the file after I create it so it shows like this: 1|2|3|4.
My Code:
a = 0
b = "|"
while a < 100000:
a += 1 # Same as a = a + 1
new = (a,b)
f = open("export.txt","a") #opens file with name of "export.txt"
f.write(str(new))
f.close()
infile = "export.txt"
outfile = "newfile.txt"
delete_list = ["(","," "'"]
fin = open(infile)
fout = open(outfile, "w+")
for line in fin:
for word in delete_list:
line = line.replace(word, "")
fout.write(line)
fin.close()
fout.close()
export.txt:
newfile.txt:

It looks like you're doing a lot of work unnecessarily.
If all you want is a file that has the numbers 0-99999 with | after each, you could do:
delim = "|"
with open('export.txt', 'w') as f:
for a in xrange(100):
f.write("%d%s" % (a, delim))
I'm not sure what the purpose of the second file is, but, in general, to open one file to read from and a second to write to, you could do:
with open('export.txt', 'r') as fi:
with open('newfile.txt', 'w') as fo:
for line in fi:
for word in line.split('|'):
print(word)
fo.write(word)
Note that there are no newlines in the original file, so for line in fi is actually reading the entire contents of "export.txt" -- this could cause issues.

Try this for writing your file:
numbers = []
for x in range(1,100001):
numbers.append(str(x))
f = open('export.txt', 'w')
f.write('|'.join(numbers))
f.close()

Python Insert text before a specific line

I want to insert a text specifically before a line 'Number'.
I want to insert 'Hello Everyone' befor the line starting with 'Number'
My code:
import re
result = []
with open("text2.txt", "r+") as f:
a = [x.rstrip() for x in f] # stores all lines from f into an array and removes "\n"
# Find the first occurance of "Centre" and store its index
for item in a:
if item.startswith("Number"): # same as your re check
break
ind = a.index(item) #here it produces index no./line no.
result.extend(a[:ind])
f.write('Hello Everyone')
tEXT FILE:
QWEW
RW
...
Number hey
Number ho
Expected output:
QWEW
RW
...
Hello Everyone
Number hey
Number ho
Please help me to fix my code:I dont get anything inserted with my text file!Please help!
Answers will be appreciated!

The problem
When you do open("text2.txt", "r"), you open your file for reading, not for writing. Therefore, nothing appears in your file.
The fix
Using r+ instead of r allows you to also write to the file (this was also pointed out in the comments. However, it overwrites, so be careful (this is an OS limitation, as described e.g. here). The following should do what you desire: It inserts "Hello everyone" into the list of lines and then overwrites the file with the updated lines.
with open("text2.txt", "r+") as f:
a = [x.rstrip() for x in f]
index = 0
for item in a:
if item.startswith("Number"):
a.insert(index, "Hello everyone") # Inserts "Hello everyone" into `a`
break
index += 1
# Go to start of file and clear it
f.seek(0)
f.truncate()
# Write each line back
for line in a:
f.write(line + "\n")

The correct answer to your problem is the hlt one, but consider also using the fileinput module:
import fileinput
found = False
for line in fileinput.input('DATA', inplace=True):
if not found and line.startswith('Number'):
print 'Hello everyone'
found = True
print line,

This is basically the same question as here: they propose to do it in three steps: read everything / insert / rewrite everything
with open("/tmp/text2.txt", "r") as f:
lines = f.readlines()
for index, line in enumerate(lines):
if line.startswith("Number"):
break
lines.insert(index, "Hello everyone !\n")
with open("/tmp/text2.txt", "w") as f:
contents = f.writelines(lines)