I am stuck on this revision exercise which asks to copy an input file to an output file and return the first and last letters.
def copy_file(filename):
input_file = open(filename, "r")
content = input_file.read()
content[0]
content[1]
return content[0] + content[-1]
input_file.close()
Why do I get an error message which I try get the first and last letters? And how would I copy the file to the output file?
Here is the test:
input_f = "FreeAdvice.txt"
first_last_chars = copy_file(input_f)
print(first_last_chars)
print_content('cure737.txt')
Error Message:
FileNotFoundError: [Errno 2] No such file or directory: 'hjac737(my username).txt'
All the code after a return statement is never executed, a proper code editor would highlight it to you, so I recommend you use one. So the file was never closed. A good practice is to use a context manager for that : it will automatically call close for you, even in case of an exception, when you exit the scope (indentation level).
The code you provided also miss to write the file content, which may be causing the error you reported.
I explicitely used the "rt" (and "wt") mode for the files (althought they are defaults), because we want the first and last character of the file, so it supports Unicode (any character, not just ASCII).
def copy_file(filename):
with open(filename, "rt") as input_file:
content = input_file.read()
print(input_file.closed) # True
my_username = "LENORMJU"
output_file_name = my_username + ".txt"
with open(output_file_name, "wt") as output_file:
output_file.write(content)
print(output_file.closed) # True
# last: return the result
return content[0] + content[-1]
print(copy_file("so67730842.py"))
When I run this script (on itself), the file is copied and I get the output d) which is correct.
I have a set of placemarks, which include quite a wide description included in its balloon within the property. Next each single description (former column header) is bounded in . Because of the shapefile naming restriction to 10 characters only.
https://gis.stackexchange.com/questions/15784/bypassing-10-character-limit-of-field-name-in-shapefiles
I have to retype most of these names manually.
Obviously, I use Notepad++, where I can swiftly press Ctrl+F and toggle Replace mode, as you can see below.
The green bounded strings were already replaced, the red ones still remain.
Basically, if I press "Replace All" then it works fine and quickly. Unfortunately, I have to go one by one. As you can see I have around 20 separate strings to "Replace all". Is there a possibility to do it quicker? Because all the .kml files are similar to each other, this is going to be the same everywhere. I need some tool, which will be able to do auto-replace for these headers cut by 10 characters limit. I think, that maybe Python tools might be helpful.
https://pythonhosted.org/pykml/
But in the tool above there is no information about bulk KML editing.
How can I set something like the "Replace All" tool for all my strings preferably if possible?
UPDATE:
I tried the code below:
files = []
with open("YesNF016.kml") as f:
for line in f.readlines():
if line[-1] == '\n':
files.append(line[:-1])
else:
files.append(line)
old_expression = 'ab'
new_expression = 'it worked'
for file in files:
new_file = ""
with open(file) as f:
for line in f.readlines():
new_file += line.replace(old_expression, new_expression)
with open(file, 'w') as f:
f.write(new_file)
The debugger shows:
[Errno 22] Invalid argument: ''
File "\test.py", line 13, in
with open(file) as f:
whereas line 13 is:
with open(file) as f:
The solutions here:
https://www.reddit.com/r/learnpython/comments/b9cljd/oserror_while_using_elementtree_to_parse_simple/
and
OSError: [Errno 22] Invalid argument Getting invalid argument while parsing xml in python
weren't helpful enough for me.
So you want to replace all occurence of X to Y in bunch of files ?
Pretty easy.
Just create a file_list.txt containing the list of files to edit.
python code:
files = []
with open("file_list.txt") as f:
for line in f.readlines():
if line[-1] == '\n':
files.append(line[:-1])
else:
files.append(line)
old_expression = 'ab'
new_expression = 'it worked'
for file in files:
new_file = ""
with open(file) as f:
for line in f.readlines():
new_file += line.replace(old_expression, new_expression)
with open(file, 'w') as f:
f.write(new_file)
Please help I need python to compare text line(s) to words like this.
with open('textfile', 'r') as f:
contents = f.readlines()
print(f_contents)
if f_contents=="a":
print("text")
I also would need it to, read a certain line, and compare that line. But when I run this program it does not do anything no error messages, nor does it print text. Also
How do you get python to write in just line 1? When I try to do it for some reason, it combines both words together can someone help thank you!
what is f_contents it's supposed to be just print(contents)after reading in each line and storing it to contents. Hope that helps :)
An example of reading a file content:
with open("criticaldocuments.txt", "r") as f:
for line in f:
print(line)
#prints all the lines in this file
#allows the user to iterate over the file line by line
OR what you want is something like this using readlines():
with open("criticaldocuments.txt", "r") as f:
contents = f.readlines()
#readlines() will store each and every line into var contents
if contents == None:
print("No lines were stored, file execution failed most likely")
elif contents == "Password is Password":
print("We cracked it")
else:
print(contents)
# this returns all the lines if no matches
Note:
contents = f.readlines()
Can be done like this too:
for line in f.readlines():
#this eliminates the ambiguity of what 'contents' is doing
#and you could work through the rest of the code the same way except
#replace the contents with 'line'.
Here is my script:
def tail(file, delay=0.5):
f = open(file, 'r')
f.seek(0, 2)
while True:
line = f.readline()
print 'line: ' + line
if not line:
time.sleep(delay)
else:
print 'line found!'
When i open the file and add some lines to it, this script is not picking it up. I am doing this on linux.
use open('filename', 'a') instead of open('filename', 'r') for adding lines to the file ... I think you actually want to append to the file rather than reading it.
The code looks fine so there is likely a buffering issue. Try using f.read(100) instead of readline so that you read whatever is available rather than searching for line endings.
I'm using Python, and would like to insert a string into a text file without deleting or copying the file. How can I do that?
Unfortunately there is no way to insert into the middle of a file without re-writing it. As previous posters have indicated, you can append to a file or overwrite part of it using seek but if you want to add stuff at the beginning or the middle, you'll have to rewrite it.
This is an operating system thing, not a Python thing. It is the same in all languages.
What I usually do is read from the file, make the modifications and write it out to a new file called myfile.txt.tmp or something like that. This is better than reading the whole file into memory because the file may be too large for that. Once the temporary file is completed, I rename it the same as the original file.
This is a good, safe way to do it because if the file write crashes or aborts for any reason, you still have your untouched original file.
Depends on what you want to do. To append you can open it with "a":
with open("foo.txt", "a") as f:
f.write("new line\n")
If you want to preprend something you have to read from the file first:
with open("foo.txt", "r+") as f:
old = f.read() # read everything in the file
f.seek(0) # rewind
f.write("new line\n" + old) # write the new line before
The fileinput module of the Python standard library will rewrite a file inplace if you use the inplace=1 parameter:
import sys
import fileinput
# replace all occurrences of 'sit' with 'SIT' and insert a line after the 5th
for i, line in enumerate(fileinput.input('lorem_ipsum.txt', inplace=1)):
sys.stdout.write(line.replace('sit', 'SIT')) # replace 'sit' and write
if i == 4: sys.stdout.write('\n') # write a blank line after the 5th line
Rewriting a file in place is often done by saving the old copy with a modified name. Unix folks add a ~ to mark the old one. Windows folks do all kinds of things -- add .bak or .old -- or rename the file entirely or put the ~ on the front of the name.
import shutil
shutil.move(afile, afile + "~")
destination= open(aFile, "w")
source= open(aFile + "~", "r")
for line in source:
destination.write(line)
if <some condition>:
destination.write(<some additional line> + "\n")
source.close()
destination.close()
Instead of shutil, you can use the following.
import os
os.rename(aFile, aFile + "~")
Python's mmap module will allow you to insert into a file. The following sample shows how it can be done in Unix (Windows mmap may be different). Note that this does not handle all error conditions and you might corrupt or lose the original file. Also, this won't handle unicode strings.
import os
from mmap import mmap
def insert(filename, str, pos):
if len(str) < 1:
# nothing to insert
return
f = open(filename, 'r+')
m = mmap(f.fileno(), os.path.getsize(filename))
origSize = m.size()
# or this could be an error
if pos > origSize:
pos = origSize
elif pos < 0:
pos = 0
m.resize(origSize + len(str))
m[pos+len(str):] = m[pos:origSize]
m[pos:pos+len(str)] = str
m.close()
f.close()
It is also possible to do this without mmap with files opened in 'r+' mode, but it is less convenient and less efficient as you'd have to read and temporarily store the contents of the file from the insertion position to EOF - which might be huge.
As mentioned by Adam you have to take your system limitations into consideration before you can decide on approach whether you have enough memory to read it all into memory replace parts of it and re-write it.
If you're dealing with a small file or have no memory issues this might help:
Option 1)
Read entire file into memory, do a regex substitution on the entire or part of the line and replace it with that line plus the extra line. You will need to make sure that the 'middle line' is unique in the file or if you have timestamps on each line this should be pretty reliable.
# open file with r+b (allow write and binary mode)
f = open("file.log", 'r+b')
# read entire content of file into memory
f_content = f.read()
# basically match middle line and replace it with itself and the extra line
f_content = re.sub(r'(middle line)', r'\1\nnew line', f_content)
# return pointer to top of file so we can re-write the content with replaced string
f.seek(0)
# clear file content
f.truncate()
# re-write the content with the updated content
f.write(f_content)
# close file
f.close()
Option 2)
Figure out middle line, and replace it with that line plus the extra line.
# open file with r+b (allow write and binary mode)
f = open("file.log" , 'r+b')
# get array of lines
f_content = f.readlines()
# get middle line
middle_line = len(f_content)/2
# overwrite middle line
f_content[middle_line] += "\nnew line"
# return pointer to top of file so we can re-write the content with replaced string
f.seek(0)
# clear file content
f.truncate()
# re-write the content with the updated content
f.write(''.join(f_content))
# close file
f.close()
Wrote a small class for doing this cleanly.
import tempfile
class FileModifierError(Exception):
pass
class FileModifier(object):
def __init__(self, fname):
self.__write_dict = {}
self.__filename = fname
self.__tempfile = tempfile.TemporaryFile()
with open(fname, 'rb') as fp:
for line in fp:
self.__tempfile.write(line)
self.__tempfile.seek(0)
def write(self, s, line_number = 'END'):
if line_number != 'END' and not isinstance(line_number, (int, float)):
raise FileModifierError("Line number %s is not a valid number" % line_number)
try:
self.__write_dict[line_number].append(s)
except KeyError:
self.__write_dict[line_number] = [s]
def writeline(self, s, line_number = 'END'):
self.write('%s\n' % s, line_number)
def writelines(self, s, line_number = 'END'):
for ln in s:
self.writeline(s, line_number)
def __popline(self, index, fp):
try:
ilines = self.__write_dict.pop(index)
for line in ilines:
fp.write(line)
except KeyError:
pass
def close(self):
self.__exit__(None, None, None)
def __enter__(self):
return self
def __exit__(self, type, value, traceback):
with open(self.__filename,'w') as fp:
for index, line in enumerate(self.__tempfile.readlines()):
self.__popline(index, fp)
fp.write(line)
for index in sorted(self.__write_dict):
for line in self.__write_dict[index]:
fp.write(line)
self.__tempfile.close()
Then you can use it this way:
with FileModifier(filename) as fp:
fp.writeline("String 1", 0)
fp.writeline("String 2", 20)
fp.writeline("String 3") # To write at the end of the file
If you know some unix you could try the following:
Notes: $ means the command prompt
Say you have a file my_data.txt with content as such:
$ cat my_data.txt
This is a data file
with all of my data in it.
Then using the os module you can use the usual sed commands
import os
# Identifiers used are:
my_data_file = "my_data.txt"
command = "sed -i 's/all/none/' my_data.txt"
# Execute the command
os.system(command)
If you aren't aware of sed, check it out, it is extremely useful.