Related
I have a CSV file that has errors. The most common one is a too early linebreak.
But now I don't know how to remove it ideally. If I read the line by line
with open("test.csv", "r") as reader:
test = reader.read().splitlines()
the wrong structure is already in my variable. Is this still the right approach and do I use a for loop over test and create a copy or can I manipulate directly in the test variable while iterating over it?
I can identify the corrupt lines by the semikolon, some rows end with a ; others start with it. So maybe counting would be an alternative way to solve it?
EDIT:
I replaced reader.read().splitlines() with reader.readlines() so I could handle the rows which end with a ;
for line in lines:
if("Foobar" in line):
line = line.replace("Foobar", "")
if(";\n" in line):
line = line.replace(";\n", ";")
The only thing that remains are rows that beginn with a ;
Since I need to go back one entry in the list
Example:
Col_a;Col_b;Col_c;Col_d
2021;Foobar;Bla
;Blub
Blub belongs in the row above.
Here's a simple Python script to merge lines until you have the desired number of fields.
import sys
sep = ';'
fields = 4
collected = []
for line in sys.stdin:
new = line.rstrip('\n').split(sep)
if collected:
collected[-1] += new[0]
collected.extend(new[1:])
else:
collected = new
if len(collected) < fields:
continue
print(';'.join(collected))
collected = []
This simply reads from standard input and prints to standard output. If the last line is incomplete, it will be lost.
The separator and the number of fields can be edited into the variables at the top; exposing these as command-line parameters left as an exercise.
If you wanted to keep the newlines, it would not be too hard to only strip a newline from the last fields, and use csv.writer to write the fields back out as properly quoted CSV.
This is how I deal with this. This function fixes the line if there are more columns than needed or if there is a line break in the middle.
Parameters of the function are:
message - content of the file - reader.read() in your case
columns - number of expected columns
filename - filename (I use it for logging)
def pre_parse(message, columns, filename):
parsed_message=[]
i =0
temp_line =''
for line in message.splitlines():
#print(line)
split = line.split(',')
if len(split) == columns:
parsed_message.append(line)
elif len(split) > columns:
print(f'Line {i} has been truncated in file {filename} - too much columns'))
split = split[:columns]
line = ','.join(split)
parsed_message.append(line)
elif len(split) < columns and temp_line =='':
temp_line = line.replace('\n','')
print(temp_line)
elif temp_line !='':
line = temp_line+line
if line.count(',') == columns-1:
print((f'Line {i} has been fixed in file {filename} - extra line feed'))
parsed_message.append(line)
temp_line =''
else:
temp_line=line.replace('\n', '')
i+=1
return parsed_message
make sure you use proper split character and proper line feed characer.
I have a stock file which looks like this:
12334232:seat belt:2.30:12:10:30
14312332:toy card:3.40:52:10:30
12512312:xbox one:5.30:23:10:30
12543243:laptop:1.34:14:10:30
65478263:banana:1.23:23:10:30
27364729:apple:4.23:42:10:30
28912382:orange:1.12:16:10:30
12892829:elephant:6.45:14:10:30
I want to replace the items in the fourth column if they are below the numbers in the fifth column after a certain transaction to the numbers in the sxith column. How would I replace the items in the fourth column?
Everytime I use the following lines of code below, it overwrites the whole file with nothing (deletes everything)
for line in stockfile:
c=line.split(":")
print("pass")
if stock_order[i] == User_list[i][0]:
stockfile.write(line.replace(current_stocklevel_list[i], reorder_order[i] ) )
else:
i = i + 1
I want the stockfile to look like this after it has replaced the necessary items in the column:
12334232:seat belt:2.30:30:10:30
14312332:toy card:3.40:30:10:30
12512312:xbox one:5.30:30:10:30
12543243:laptop:1.34:30::10:30
65478263:banana:1.23:30:10:30
27364729:apple:4.23:30:10:30
28912382:orange:1.12:30:10:30
12892829:elephant:6.45:30:10:30
If you are opening file after some time, you should use "a" (append) as a mode so that file doesn't get truncated.
Write pointer will automatically be on the end of file.
So:
f = open("filename", "a")
f.seek(0) # To start from beginning
But if you want to read and write, then add "+" to the mode and file wouldn't be truncated as well.
f = open("filename", "r+")
Both read and write pointers will be at the beginning of file, you'll need to seek only onto position where you wish to start writing/reading.
But you are doing it wrong.
See, file's content will be overwritten, not inserted automatically.
If you are in writable mode and at the end of file content will be added.
So, you either need to load whole file, make changes you need and write everything back.
Or, you have to write changes at some point and shift remaining content truncating the file if the content is shorter than before.
mmap module can help you to treat file as a string,. You will be able to efficiently shift data and to resize the file.
But, if you really want to change file in place, you should have the file with fixed length of columns. So, when you want to change a value, you do not need to shift anything back and forth. Just find the right row and col, seek there, write new value over the old one (making sure to delete all of the old) and that is just that.
You should try to read in the data first:
with open('inputfile', 'r') as infile:
data = infile.readlines()
Then you can loop over the data and edit as needed and write it out:
with open('outputfile', 'w') as outfile:
for line in data:
c = line.split(":")
if random.randint(1,3) == 1:
# update fourth column based on some good reason
c[3] += 2
outfile.write(':'.join(c) + '\n')
Or you could do it on go with something like:
with open('inputfile', 'r') as infile, open('outputfile', 'w') as outfile:
line = infile.readline()
c = line.split(":")
if random.randint(1,3) == 1:
# update fourth column based on some good reason
c[3] += 2
outfile.write(':'.join(c) + '\n')
os.rename('outputfile', 'inputfile')
Is there a way to do this? Say I have a file that's a list of names that goes like this:
Alfred
Bill
Donald
How could I insert the third name, "Charlie", at line x (in this case 3), and automatically send all others down one line? I've seen other questions like this, but they didn't get helpful answers. Can it be done, preferably with either a method or a loop?
This is a way of doing the trick.
with open("path_to_file", "r") as f:
contents = f.readlines()
contents.insert(index, value)
with open("path_to_file", "w") as f:
contents = "".join(contents)
f.write(contents)
index and value are the line and value of your choice, lines starting from 0.
If you want to search a file for a substring and add a new text to the next line, one of the elegant ways to do it is the following:
import os, fileinput
old = "A"
new = "B"
for line in fileinput.FileInput(file_path, inplace=True):
if old in line :
line += new + os.linesep
print(line, end="")
There is a combination of techniques which I found useful in solving this issue:
with open(file, 'r+') as fd:
contents = fd.readlines()
contents.insert(index, new_string) # new_string should end in a newline
fd.seek(0) # readlines consumes the iterator, so we need to start over
fd.writelines(contents) # No need to truncate as we are increasing filesize
In our particular application, we wanted to add it after a certain string:
with open(file, 'r+') as fd:
contents = fd.readlines()
if match_string in contents[-1]: # Handle last line to prevent IndexError
contents.append(insert_string)
else:
for index, line in enumerate(contents):
if match_string in line and insert_string not in contents[index + 1]:
contents.insert(index + 1, insert_string)
break
fd.seek(0)
fd.writelines(contents)
If you want it to insert the string after every instance of the match, instead of just the first, remove the else: (and properly unindent) and the break.
Note also that the and insert_string not in contents[index + 1]: prevents it from adding more than one copy after the match_string, so it's safe to run repeatedly.
You can just read the data into a list and insert the new record where you want.
names = []
with open('names.txt', 'r+') as fd:
for line in fd:
names.append(line.split(' ')[-1].strip())
names.insert(2, "Charlie") # element 2 will be 3. in your list
fd.seek(0)
fd.truncate()
for i in xrange(len(names)):
fd.write("%d. %s\n" %(i + 1, names[i]))
The accepted answer has to load the whole file into memory, which doesn't work nicely for large files. The following solution writes the file contents with the new data inserted into the right line to a temporary file in the same directory (so on the same file system), only reading small chunks from the source file at a time. It then overwrites the source file with the contents of the temporary file in an efficient way (Python 3.8+).
from pathlib import Path
from shutil import copyfile
from tempfile import NamedTemporaryFile
sourcefile = Path("/path/to/source").resolve()
insert_lineno = 152 # The line to insert the new data into.
insert_data = "..." # Some string to insert.
with sourcefile.open(mode="r") as source:
destination = NamedTemporaryFile(mode="w", dir=str(sourcefile.parent))
lineno = 1
while lineno < insert_lineno:
destination.file.write(source.readline())
lineno += 1
# Insert the new data.
destination.file.write(insert_data)
# Write the rest in chunks.
while True:
data = source.read(1024)
if not data:
break
destination.file.write(data)
# Finish writing data.
destination.flush()
# Overwrite the original file's contents with that of the temporary file.
# This uses a memory-optimised copy operation starting from Python 3.8.
copyfile(destination.name, str(sourcefile))
# Delete the temporary file.
destination.close()
EDIT 2020-09-08: I just found an answer on Code Review that does something similar to above with more explanation - it might be useful to some.
You don't show us what the output should look like, so one possible interpretation is that you want this as the output:
Alfred
Bill
Charlie
Donald
(Insert Charlie, then add 1 to all subsequent lines.) Here's one possible solution:
def insert_line(input_stream, pos, new_name, output_stream):
inserted = False
for line in input_stream:
number, name = parse_line(line)
if number == pos:
print >> output_stream, format_line(number, new_name)
inserted = True
print >> output_stream, format_line(number if not inserted else (number + 1), name)
def parse_line(line):
number_str, name = line.strip().split()
return (get_number(number_str), name)
def get_number(number_str):
return int(number_str.split('.')[0])
def format_line(number, name):
return add_dot(number) + ' ' + name
def add_dot(number):
return str(number) + '.'
input_stream = open('input.txt', 'r')
output_stream = open('output.txt', 'w')
insert_line(input_stream, 3, 'Charlie', output_stream)
input_stream.close()
output_stream.close()
Parse the file into a python list using file.readlines() or file.read().split('\n')
Identify the position where you have to insert a new line, according to your criteria.
Insert a new list element there using list.insert().
Write the result to the file.
location_of_line = 0
with open(filename, 'r') as file_you_want_to_read:
#readlines in file and put in a list
contents = file_you_want_to_read.readlines()
#find location of what line you want to insert after
for index, line in enumerate(contents):
if line.startswith('whatever you are looking for')
location_of_line = index
#now you have a list of every line in that file
context.insert(location_of_line, "whatever you want to append to middle of file")
with open(filename, 'w') as file_to_write_to:
file_to_write_to.writelines(contents)
That is how I ended up getting whatever data I want to insert to the middle of the file.
this is just pseudo code, as I was having a hard time finding clear understanding of what is going on.
essentially you read in the file to its entirety and add it into a list, then you insert your lines that you want to that list, and then re-write to the same file.
i am sure there are better ways to do this, may not be efficient, but it makes more sense to me at least, I hope it makes sense to someone else.
A simple but not efficient way is to read the whole content, change it and then rewrite it:
line_index = 3
lines = None
with open('file.txt', 'r') as file_handler:
lines = file_handler.readlines()
lines.insert(line_index, 'Charlie')
with open('file.txt', 'w') as file_handler:
file_handler.writelines(lines)
I write this in order to reutilize/correct martincho's answer (accepted one)
! IMPORTANT: This code loads all the file into ram and rewrites content to the file
Variables index, value may be what you desire, but pay attention to making value string and end with '\n' if you don't want it to mess with existing data.
with open("path_to_file", "r+") as f:
# Read the content into a variable
contents = f.readlines()
contents.insert(index, value)
# Reset the reader's location (in bytes)
f.seek(0)
# Rewrite the content to the file
f.writelines(contents)
See the python docs about file.seek method: Python docs
Below is a slightly awkward solution for the special case in which you are creating the original file yourself and happen to know the insertion location (e.g. you know ahead of time that you will need to insert a line with an additional name before the third line, but won't know the name until after you've fetched and written the rest of the names). Reading, storing and then re-writing the entire contents of the file as described in other answers is, I think, more elegant than this option, but may be undesirable for large files.
You can leave a buffer of invisible null characters ('\0') at the insertion location to be overwritten later:
num_names = 1_000_000 # Enough data to make storing in a list unideal
max_len = 20 # The maximum allowed length of the inserted line
line_to_insert = 2 # The third line is at index 2 (0-based indexing)
with open(filename, 'w+') as file:
for i in range(line_to_insert):
name = get_name(i) # Returns 'Alfred' for i = 0, etc.
file.write(F'{i + 1}. {name}\n')
insert_position = file.tell() # Position to jump back to for insertion
file.write('\0' * max_len + '\n') # Buffer will show up as a blank line
for i in range(line_to_insert, num_names):
name = get_name(i)
file.write(F'{i + 2}. {name}\n') # Line numbering now bumped up by 1.
# Later, once you have the name to insert...
with open(filename, 'r+') as file: # Must use 'r+' to write to middle of file
file.seek(insert_position) # Move stream to the insertion line
name = get_bonus_name() # This lucky winner jumps up to 3rd place
new_line = F'{line_to_insert + 1}. {name}'
file.write(new_line[:max_len]) # Slice so you don't overwrite next line
Unfortunately there is no way to delete-without-replacement any excess null characters that did not get overwritten (or in general any characters anywhere in the middle of a file), unless you then re-write everything that follows. But the null characters will not affect how your file looks to a human (they have zero width).
Is there a way to do this? Say I have a file that's a list of names that goes like this:
Alfred
Bill
Donald
How could I insert the third name, "Charlie", at line x (in this case 3), and automatically send all others down one line? I've seen other questions like this, but they didn't get helpful answers. Can it be done, preferably with either a method or a loop?
This is a way of doing the trick.
with open("path_to_file", "r") as f:
contents = f.readlines()
contents.insert(index, value)
with open("path_to_file", "w") as f:
contents = "".join(contents)
f.write(contents)
index and value are the line and value of your choice, lines starting from 0.
If you want to search a file for a substring and add a new text to the next line, one of the elegant ways to do it is the following:
import os, fileinput
old = "A"
new = "B"
for line in fileinput.FileInput(file_path, inplace=True):
if old in line :
line += new + os.linesep
print(line, end="")
There is a combination of techniques which I found useful in solving this issue:
with open(file, 'r+') as fd:
contents = fd.readlines()
contents.insert(index, new_string) # new_string should end in a newline
fd.seek(0) # readlines consumes the iterator, so we need to start over
fd.writelines(contents) # No need to truncate as we are increasing filesize
In our particular application, we wanted to add it after a certain string:
with open(file, 'r+') as fd:
contents = fd.readlines()
if match_string in contents[-1]: # Handle last line to prevent IndexError
contents.append(insert_string)
else:
for index, line in enumerate(contents):
if match_string in line and insert_string not in contents[index + 1]:
contents.insert(index + 1, insert_string)
break
fd.seek(0)
fd.writelines(contents)
If you want it to insert the string after every instance of the match, instead of just the first, remove the else: (and properly unindent) and the break.
Note also that the and insert_string not in contents[index + 1]: prevents it from adding more than one copy after the match_string, so it's safe to run repeatedly.
You can just read the data into a list and insert the new record where you want.
names = []
with open('names.txt', 'r+') as fd:
for line in fd:
names.append(line.split(' ')[-1].strip())
names.insert(2, "Charlie") # element 2 will be 3. in your list
fd.seek(0)
fd.truncate()
for i in xrange(len(names)):
fd.write("%d. %s\n" %(i + 1, names[i]))
The accepted answer has to load the whole file into memory, which doesn't work nicely for large files. The following solution writes the file contents with the new data inserted into the right line to a temporary file in the same directory (so on the same file system), only reading small chunks from the source file at a time. It then overwrites the source file with the contents of the temporary file in an efficient way (Python 3.8+).
from pathlib import Path
from shutil import copyfile
from tempfile import NamedTemporaryFile
sourcefile = Path("/path/to/source").resolve()
insert_lineno = 152 # The line to insert the new data into.
insert_data = "..." # Some string to insert.
with sourcefile.open(mode="r") as source:
destination = NamedTemporaryFile(mode="w", dir=str(sourcefile.parent))
lineno = 1
while lineno < insert_lineno:
destination.file.write(source.readline())
lineno += 1
# Insert the new data.
destination.file.write(insert_data)
# Write the rest in chunks.
while True:
data = source.read(1024)
if not data:
break
destination.file.write(data)
# Finish writing data.
destination.flush()
# Overwrite the original file's contents with that of the temporary file.
# This uses a memory-optimised copy operation starting from Python 3.8.
copyfile(destination.name, str(sourcefile))
# Delete the temporary file.
destination.close()
EDIT 2020-09-08: I just found an answer on Code Review that does something similar to above with more explanation - it might be useful to some.
You don't show us what the output should look like, so one possible interpretation is that you want this as the output:
Alfred
Bill
Charlie
Donald
(Insert Charlie, then add 1 to all subsequent lines.) Here's one possible solution:
def insert_line(input_stream, pos, new_name, output_stream):
inserted = False
for line in input_stream:
number, name = parse_line(line)
if number == pos:
print >> output_stream, format_line(number, new_name)
inserted = True
print >> output_stream, format_line(number if not inserted else (number + 1), name)
def parse_line(line):
number_str, name = line.strip().split()
return (get_number(number_str), name)
def get_number(number_str):
return int(number_str.split('.')[0])
def format_line(number, name):
return add_dot(number) + ' ' + name
def add_dot(number):
return str(number) + '.'
input_stream = open('input.txt', 'r')
output_stream = open('output.txt', 'w')
insert_line(input_stream, 3, 'Charlie', output_stream)
input_stream.close()
output_stream.close()
Parse the file into a python list using file.readlines() or file.read().split('\n')
Identify the position where you have to insert a new line, according to your criteria.
Insert a new list element there using list.insert().
Write the result to the file.
location_of_line = 0
with open(filename, 'r') as file_you_want_to_read:
#readlines in file and put in a list
contents = file_you_want_to_read.readlines()
#find location of what line you want to insert after
for index, line in enumerate(contents):
if line.startswith('whatever you are looking for')
location_of_line = index
#now you have a list of every line in that file
context.insert(location_of_line, "whatever you want to append to middle of file")
with open(filename, 'w') as file_to_write_to:
file_to_write_to.writelines(contents)
That is how I ended up getting whatever data I want to insert to the middle of the file.
this is just pseudo code, as I was having a hard time finding clear understanding of what is going on.
essentially you read in the file to its entirety and add it into a list, then you insert your lines that you want to that list, and then re-write to the same file.
i am sure there are better ways to do this, may not be efficient, but it makes more sense to me at least, I hope it makes sense to someone else.
A simple but not efficient way is to read the whole content, change it and then rewrite it:
line_index = 3
lines = None
with open('file.txt', 'r') as file_handler:
lines = file_handler.readlines()
lines.insert(line_index, 'Charlie')
with open('file.txt', 'w') as file_handler:
file_handler.writelines(lines)
I write this in order to reutilize/correct martincho's answer (accepted one)
! IMPORTANT: This code loads all the file into ram and rewrites content to the file
Variables index, value may be what you desire, but pay attention to making value string and end with '\n' if you don't want it to mess with existing data.
with open("path_to_file", "r+") as f:
# Read the content into a variable
contents = f.readlines()
contents.insert(index, value)
# Reset the reader's location (in bytes)
f.seek(0)
# Rewrite the content to the file
f.writelines(contents)
See the python docs about file.seek method: Python docs
Below is a slightly awkward solution for the special case in which you are creating the original file yourself and happen to know the insertion location (e.g. you know ahead of time that you will need to insert a line with an additional name before the third line, but won't know the name until after you've fetched and written the rest of the names). Reading, storing and then re-writing the entire contents of the file as described in other answers is, I think, more elegant than this option, but may be undesirable for large files.
You can leave a buffer of invisible null characters ('\0') at the insertion location to be overwritten later:
num_names = 1_000_000 # Enough data to make storing in a list unideal
max_len = 20 # The maximum allowed length of the inserted line
line_to_insert = 2 # The third line is at index 2 (0-based indexing)
with open(filename, 'w+') as file:
for i in range(line_to_insert):
name = get_name(i) # Returns 'Alfred' for i = 0, etc.
file.write(F'{i + 1}. {name}\n')
insert_position = file.tell() # Position to jump back to for insertion
file.write('\0' * max_len + '\n') # Buffer will show up as a blank line
for i in range(line_to_insert, num_names):
name = get_name(i)
file.write(F'{i + 2}. {name}\n') # Line numbering now bumped up by 1.
# Later, once you have the name to insert...
with open(filename, 'r+') as file: # Must use 'r+' to write to middle of file
file.seek(insert_position) # Move stream to the insertion line
name = get_bonus_name() # This lucky winner jumps up to 3rd place
new_line = F'{line_to_insert + 1}. {name}'
file.write(new_line[:max_len]) # Slice so you don't overwrite next line
Unfortunately there is no way to delete-without-replacement any excess null characters that did not get overwritten (or in general any characters anywhere in the middle of a file), unless you then re-write everything that follows. But the null characters will not affect how your file looks to a human (they have zero width).
I'd like to remove the first column from a file. The file contains 3 columns separated by space and the columns has the following titles:
X', 'Displacement' and 'Force' (Please see the image).
I have came up with the following code, but to my disappointment it doesn't work!
f = open("datafile.txt", 'w')
for line in f:
line = line.split()
del x[0]
f.close()
Any help is much appreciated !
Esan
First of all, you're attempting to read from a file (by iterating through the file contents) that is open for writing. This will give you an IOError.
Second, there is no variable named x in existence (you have not declared/set one in the script). This will generate a NameError.
Thirdly and finally, once you have finished (correctly) reading and editing the columns in your file, you will need to write the data back into the file.
To avoid loading a (potentially large) file into memory all at once, it is probably a good idea to read from one file (line by line) and write to a new file simultaneously.
Something like this might work:
f = open("datafile.txt", "r")
g = open("datafile_fixed.txt", "w")
for line in f:
if line.strip():
g.write("\t".join(line.split()[1:]) + "\n")
f.close()
g.close()
Some reading about python i/o might be helpful, but something like the following should get you on your feet:
with open("datafile.txt", "r") as fin:
with open("outputfile.txt", "w") as fout:
for line in fin:
line = line.split(' ')
if len(line) == 3:
del line[0]
fout.write(line[0] + ' ' + line[1])
else:
fout.write('\n')
EDIT: fixed to work with blank lines
print ''.join([' '.join(l.split()[1:]) for l in file('datafile.txt')])
or, if you want to preserve spaces and you know that the second column always starts at the, say, 10th character:
print ''.join([l[11:] for l in file('datafile.txt')])