I am trying to delete a line from a text file after opening it and without storing it in any list variable using f.readlines() or anything like that.
I dont have an option to open the file and store the contents in a variable and make some changes and write them to another file or any kind of operations that would require to open the file and store them again in a list variable and make some changes and store them back to the file. The file is being constantly appended by some other program, so I cannot do any kind of that stuff.
I am using f.seek() to reset the pointer to the beginning of the file, and using f.readline() as well as f.tell() to know the length of the first line. After that I am trying to replace each character with a blank space using while loop.
pos=0
eol = 0
ll=0
with open('file1.txt','rb+') as f:
f.seek(pos,1) #position at the beginning of the file
print(f.readline()) #reading the first line
pos = f.tell() #storing the length of first line
#the while loop will run from 0 to pos and replace every character with blank space
while eol != pos:
with open('file1.txt','rb+') as f:
f.seek(eol,1)
f.write(b' ')
eol += 1 #incrementing the eol variable to move the file pointer to next character
the code is working fine but with one problem which I cant figure out what,
for example if this is the original file
file1.txt
this is line 1
this is line 2
this is line 3
after running the program , my output is
this is line 2
this is line 3
the first line is getting deleted but there is a bunch of white space in front of the 2nd line.
Maybe I am missing a simple logic here.
Any help will be appreciated.
Thank you
Update :
If i have understood it correctly I have changed the code and made it like this, and instead of b' ' i am putting '\r' as carraige return, which resulted in this :
the code :
while eol != pos-1:
with open('file1.txt','rb+') as f:
f.seek(eol,0)
f.write(b'\r')
eol += 1
the result :
original :
this is line 1
this is line 2
this is line 3
after execution
this is line 2
this is line 3
you see the 1st line is removed but followed with '\r'
Related
I have a text file with the following contents:
1 a 20
2 b 30
3 c 40
I need to check if the first character of a particular line is 2 and edit its final two characters to 12, and rewrite the data into the file. New file should look something like this:
1 a 20
2 b 12
3 c 40
Need help doing this in python 3.
Couldn't figure it out. Help.
To modify contents of a file with python you will need to open the file in read mode to extract the contents of the file. You can then make changes on the extracted contents. To make your changes permanent, you have to write the contents back to the file.
The whole process looks something like this:
from pathlib import Path
# Define path to your file
your_file = Path("your_file.txt")
# Read the data in your file
with your_file.open('r') as f:
lines = f.readlines()
# Edit lines that start with a "2"
for i in range(len(lines)):
if lines[i].startswith("2"):
lines[i] = lines[i][:-3] + "12\n"
# Write data back to file
with your_file.open('w') as f:
f.writelines(lines)
Note that in order to change the last two characters of a string, you actually need to change the two characters before the last. This is because of the newline character, which indicates that the line has ended and new characters should be put on the line below. The \n you see after 12 is the newline character. If you don't put this in your replacement string, what originally was the next string will be put directly behind your replacement.
The question:
Write a function file_size(filename) that returns a count of the number of characters in the file whose name is given as a parameter. You may assume that when being tested in this CodeRunner question your function will never be called with a non-existent filename.
For example, if data.txt is a file containing just the following line: Hi there!
A call to file_size('data.txt') should return the value 10. This includes the newline character that will be added to the line when you're creating the file (be sure to hit the 'Enter' key at the end of each line).
What I have tried:
def file_size(data):
"""Count the number of characters in a file"""
infile = open('data.txt')
data = infile.read()
infile.close()
return len(data)
print(file_size('data.txt'))
# data.txt contains 'Hi there!' followed by a new line
character.
I get the correct answer for this file however I fail a test that users a larger/longer file which should have a character count of 81 but I still get 10. I am trying to get the code to count the correct size of any file.
Firstly, I would like to say that I am newbie in Python.
I will ll try to explain my problem as best as I can.
The main aim of the code is to be able to read, modify and copy a txt file.
In order to do that I would like to split the problem up in three different steps.
1 - Copy the first N lines into a new txt file (CopyFile), exactly as they are in the original file (OrigFile)
2 - Access to a specific line where I want to change a float number for other. I want to append this line to CopyFile.
3 - Copy the rest of the OrigFile from line in point 2 to the end of the file.
At the moment I have been able to do step 1 with next code:
with open("OrigFile.txt") as myfile:
head = [next(myfile) for x iin range(10)] #read first 10 lines of txt file
copy = open("CopyFile.txt", "w") #create a txt file named CopyFile.txt
copy.write("".join(head)) #convert list into str
copy.close #close txt file
For the second step, my idea is to access directly to the txt line I am interested in and recognize the float number I would like to change. Code:
line11 = linecache.getline("OrigFile.txt", 11) #opening and accessing directly to line 11
FltNmb = re.findall("\d+\.\d+", line11) #regular expressions to identify float numbers
My problem comes when I need to change FltNmb for a new one, taking into consideration that I need to specify it inside the line11. How could I achieve that?
Open both files and write each line sequentially while incrementing line counter.
Condition for line 11 to replace the float number. Rest of the lines are written without modifications:
with open("CopyFile.txt", "w") as newfile:
with open("OrigFile.txt") as myfile:
linecounter = 1
for line in myfile:
if linecounter == 11:
newline = re.sub("^(\d+\.\d+)", "<new number>", line)
linecounter += 1
outfile.write(newline)
else:
newfile.write(line)
linecounter += 1
Here is a snippet from a text file I am working on.
http://pastebin.com/4Uba5i4P
I would like to use python to detect those big repeating "~ Move" lines (Which are not identical except for the "~ Move" part.), and remove all but the first and last of those lines.
How I would I start to go about this?
You could read the file line by line like this:
`## Open the file with read only permit
f = open('myTextFile.txt')
## Read the first line
line = f.readline()
## If the file is not empty keep reading line one at a time #
# till the file is empty while line: print line
line = f.readline() f.close()`
With this you could then edit this sample to test each line using a regex like this:
`if line.find("~Move") == -1:
Break;
Else:
Line=Line [5:-1]`
Though this assumes that the ~Move is all at the beginning of the line. Hope this helps, if not leave a comment and I'll try and help.
Can you explain what is going on in this code? I don't seem to understand
how you can open the file and read it line by line instead of all of the sentences at the same time in a for loop. Thanks
Let's say I have these sentences in a document file:
cat:dog:mice
cat1:dog1:mice1
cat2:dog2:mice2
cat3:dog3:mice3
Here is the code:
from sys import argv
filename = input("Please enter the name of a file: ")
f = open(filename,'r')
d1ct = dict()
print("Number of times each animal visited each station:")
print("Animal Id Station 1 Station 2")
for line in f:
if '\n' == line[-1]:
line = line[:-1]
(AnimalId, Timestamp, StationId,) = line.split(':')
key = (AnimalId,StationId,)
if key not in d1ct:
d1ct[key] = 0
d1ct[key] += 1
The magic is at:
for line in f:
if '\n' == line[-1]:
line = line[:-1]
Python file objects are special in that they can be iterated over in a for loop. On each iteration, it retrieves the next line of the file. Because it includes the last character in the line, which could be a newline, it's often useful to check and remove the last character.
As Moshe wrote, open file objects can be iterated. Only, they are not of the file type in Python 3.x (as they were in Python 2.x). If the file object is opened in text mode, then the unit of iteration is one text line including the \n.
You can use line = line.rstrip() to remove the \n plus the trailing withespaces.
If you want to read the content of the file at once (into a multiline string), you can use content = f.read().
There is a minor bug in the code. The open file should always be closed. I means to use f.close() after the for loop. Or you can wrap the open to the newer with construct that will close the file for you -- I suggest to get used to the later approach.