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How to read line in text file and replace the whole line in Python?

I want to replace a whole line in a text document, if there is a line that begins with "truck_placement"
Can I remove the whole line when it contains "truck_placement" and then write the new text?
I tried it but it only inserts the new text und doesn't replace the whole line.
Thats the current code:
cordget = coordinatesentry.get()
fin = open(save_file,"r")
filedata = fin.read()
fin.close
newdata = filedata.replace("truck_placement: " , "truck_placement: " + cordget)
fin = open(save_file, "w")
fin.write(newdata)
fin.close

Your best bet is to append all the lines without "truck_placement" to a new file. This can be done with the following code:
original = open("truck.txt","r")
new = open("new_truck.txt","a")
for line in original:
if "truck_placement" not in line:
new.write(line)
original.close()
new.close()

You can either read the whole file into one string and replace the line using regular expression:
import re
cordget = "(value, one) (value, two)"
save_file = "sample.txt"
with open(save_file, "r") as f:
data = f.read()
# Catch the line from "truck_placement: " until the newline character ('\n')
# and replace it with the second argument, where '\1' the catched group
# "truck_placement: " is.
data = re.sub(r'(truck_placement: ).*\n', r'\1%s\n' % cordget, data)
with open(save_file, "w") as f:
f.writelines(data)
Or you could read the file as a list of all lines and overwrite the specific line:
cordget = "(value, one) (value, two)"
save_file = "sample.txt"
with open(save_file, "r") as f:
data = f.readlines()
for index, line in enumerate(data):
if "truck_placement" in line:
data[index] = f"truck_placement: {cordget}\n"
with open(save_file, "w") as f:
f.writelines(data)

How do you replace a specific line of a file with python?

line_row = -1
file = open(file_path, 'r')
for number_of_lines in file:
line_row = line_row + 1
if '1234' in number_of_lines:
lines = file.readlines()
line = lines[line_row]
print(lines)
lines[line_row] = 'hello'
file = open(file_path, "w")
file.writelines(lines)
file.close()
When I run this, it will delete everything that is before the nth line. I want it to replace only the nth line. can you help me?

try this, using enumerate
with open(file_path, 'r') as f:
lines = f.readlines()
for i, line in enumerate(lines):
if "some text" in line:
lines[i] = "updated text"
with open(file_path, "w") as f:
f.writelines(lines)

I need to search a string in data file. but the string is written in another file

I have key words to be search in one file let say abc.txt and in another file I have my data, def.txt.
I want a code in python to find key words written in abc.txt, in def.txt and if present, print those line in a new file.
Thank you.
I tried writing a code but it didn't work.
following is the code I write.
f = open('/home/vivek/Documents/abc.txt')
f1 = open('output.txt', 'a')
f2 = open('/home/vivek/Documents/def.txt', 'r')
# doIHaveToCopyTheLine=False
for line in f.readlines():
if f2 in line:
f1.write(line)
f1.close()
f.close()
f2.close()

Load the keywords into a list then you can check the other file line-by-line, and write to outfile as you find keywords in the line.
with open('/path/to/keywords.txt') as f:
keywords = set(line.strip() for line in f) # assuming words are separated by line
with open('/path/to/search_me.txt') as f, open('/path/to/outfile.txt', 'w') as outfile:
for line in f:
if any(kw in line for kw in keywords):
outfile.write(line)

You should record all the words in abc.txt use a set and then search them in def.txt
word_set = set()
with open('/home/vivek/Documents/abc.txt') as f:
for line in f:
word_set.add(line.strip())
f1 = open('output.txt', 'a')
with open('/home/vivek/Documents/def.txt') as f:
for line in f:
find = False
for word in word_set:
if word in line:
find = True
break
if find:
f1.write(line)
f1.close()

You can try this code:
with open("keyword.txt", "r") as keyword_file:
keywords = keyword_file.read().strip()
keywords = keywords.split()
with open("data.txt", "r") as data_file, open("output.txt", "w") as output_file:
for line in data_file.readlines():
line = line.strip()
for word in keywords:
if line.find(word) != -1:
print line
output_file.writelines(line + '\n')
break

In addition to sytech's answer you may try this:
with open('def.txt') as kw_obj, open('abc.txt') as in_obj:
keywords = set(kw_obj.read().split())
in_lines = in_obj.readlines()
match_lines = [line for keyword in keywords for line in in_lines if keyword in line]
if match_lines:
with open('out.txt', 'w') as out:
out.write(''.join(match_lines))

how to read the content of .txt file using python?

output_filename = r"C:\Users\guage\Output.txt"
RRA:
GREQ-299684_6j
GREQ-299684_6k
CZM:
V-GREQ-299684_6k
V-GREQ-299524_9
F_65624_1
R-GREQ-299680_5
DUN:
FB_71125_1
FR:
VQ-299659_18
VR-GREQ-299659_19
VEQ-299659_28
VR-GREQ-299659_31
VR-GREQ-299659_32
VEQ-299576_1
GED:
VEQ-299622_2
VR-GREQ-299618_13
VR-GREQ-299559_1
VR-GREQ-299524_14
FB_65624_1
VR-GREQ-299645_1
MNT:
FB_71125_1
FB_71125_2
VR-534_4
The above is the content of the the .txt file. how can I read it separately the content of it. for example -
RRA:VR-GREQ-299684_6j VR-GREQ-299684_6k VR-GREQ-299606_3 VR-GREQ-299606_4 VR-GREQ-299606_5 VR-GREQ-299606_7
and save it in a variable or something similar to it. Later I want to read CZM separately and so on. I did as below.
with open(output_filename, 'r') as f:
excel = f.read()
But how to read it separately ? can someone tell me how to do it ?

Something like this:
def read_file_with_custom_record_separator(file_path, delimiter='\n'):
fh = open(file_path)
data = ""
for line in fh:
if line.strip().endswith(delimiter) and data != "":
print "VARIABLE:\n<", data, ">\n"
data = line
else:
data += line
print "LAST VARIABLE:\n<", data, ">\n"
And then:
read_file_with_custom_record_separator("input.txt", ":")

You can make use of the file text : as indicator to create a new file like this:
savefilename = ""
with open(filename, 'r') as f:
for line in f:
line = line.strip() # get rid of the unnecessary white chars
lastchar = line[-1:] # get the last char
if lastchar == ":": # if the last char is ":"
savefilename = line[0:-1] # get file name from line (except the ":")
sf = open(savefilename + ".txt", 'w') # create a new file
else:
sf.write(line + "\n") # write the data to the opened file
Then you should get collection of files:
RRA.txt
CZM.txt
DUN.txt
# etc
which contains all the appropriate data:
RRA.txt
VR-GREQ-299684_6j
VR-GREQ-299684_6k
VR-GREQ-299606_3
VR-GREQ-299606_4
VR-GREQ-299606_5
VR-GREQ-299606_7
CZM.txt
VR-GREQ-299684_6k
VR-GREQ-299606_6
VR-GREQ-299606_8
VR-GREQ-299640_1
VR-GREQ-299640_5
VR-GREQ-299524_9
FB_65624_1
VR-GREQ-299680_5
DUN.txt
FB_71125_1
# and so on
You can replace the sf = open and the sf.write which whatever way you feel best to separate the data. Here, I use files...

You can iterate over the file and use the lines and indices to your advantage; something like this:
with open(output_filename, 'r') as f:
for index, line in enumerate(f):
# here you have access to each line and its index
# so you can save any number of lines you wish

What about reading it into a list, then process its element as you prefer
>>> f = open('myfile.txt', 'r').readlines()
>>> len(f)
46
>>> f[0]
RRA:
>>> f[-1]
VR-GREQ-299534_4
>>> f[:3]
['RRA:\n', 'VR-GREQ-299684_6j \n', 'VR-GREQ-299684_6k \n']
>>>
>>> [l for l in f if l.startswith('FB_')]
['FB_65624_1 \n', 'FB_71125_1 \n', 'FB_69228_1 \n', 'FB_65624_1 \n', 'FB_71125_1 \n', 'FB_71125_2 \n']
>>>

Match the last word and delete the entire line

Input.txt File
12626232 : Bookmarks
1321121:
126262
Here 126262: can be anything text or digit, so basically will search for last word is : (colon) and delete the entire line
Output.txt File
12626232 : Bookmarks
My Code:
def function_example():
fn = 'input.txt'
f = open(fn)
output = []
for line in f:
if not ":" in line:
output.append(line)
f.close()
f = open(fn, 'w')
f.writelines(output)
f.close()
Problem: When I match with : it remove the entire line, but I just want to check if it is exist in the end of line and if it is end of the line then only remove the entire line.
Any suggestion will be appreciated. Thanks.
I saw as following but not sure how to use it in here
a = "abc here we go:"
print a[:-1]

I believe with this you should be able to achieve what you want.
with open(fname) as f:
lines = f.readlines()
for line in lines:
if not line.strip().endswith(':'):
print line
Here fname is the variable pointing to the file location.

You were almost there with your function. You were checking if : appears anywhere in the line, when you need to check if the line ends with it:
def function_example():
fn = 'input.txt'
f = open(fn)
output = []
for line in f:
if not line.strip().endswith(":"): # This is what you were missing
output.append(line)
f.close()
f = open(fn, 'w')
f.writelines(output)
f.close()
You could have also done if not line.strip()[:-1] == ':':, but endswith() is better suited for your use case.
Here is a compact way to do what you are doing above:
def function_example(infile, outfile, limiter=':'):
''' Filters all lines in :infile: that end in :limiter:
and writes the remaining lines to :outfile: '''
with open(infile) as in, open(outfile,'w') as out:
for line in in:
if not line.strip().endswith(limiter):
out.write(line)
The with statement creates a context and automatically closes files when the block ends.

To search if the last letter is : Do following
if line.strip().endswith(':'):
...Do Something...

You can use a regular expression
import re
#Something end with ':'
regex = re.compile('.(:+)')
new_lines = []
file_name = "path_to_file"
with open(file_name) as _file:
lines = _file.readlines()
new_lines = [line for line in lines if regex.search(line.strip())]
with open(file_name, "w") as _file:
_file.writelines(new_lines)