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Updating file using Python
Most efficient way to modify the last line of a large text file in PythonHow to merge two dictionaries in a single expression?How do I check whether a file exists without exceptions?Calling an external command in PythonWhat are metaclasses in Python?How do I tell if a regular file does not exist in Bash?How to get line count cheaply in Python?Find and restore a deleted file in a Git repositoryHow to read a file line-by-line into a list?Does Python have a string 'contains' substring method?Why is reading lines from stdin much slower in C++ than Python?
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I know the normal way to write to a file by rewriting the lines except the ones to delete. But I want to know is there an efficient way to delete or update a line in place or append at the last in a file using file pointers in Python.
python python-3.x file-io file-handling
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
add a comment |
I know the normal way to write to a file by rewriting the lines except the ones to delete. But I want to know is there an efficient way to delete or update a line in place or append at the last in a file using file pointers in Python.
python python-3.x file-io file-handling
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
add a comment |
I know the normal way to write to a file by rewriting the lines except the ones to delete. But I want to know is there an efficient way to delete or update a line in place or append at the last in a file using file pointers in Python.
python python-3.x file-io file-handling
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
I know the normal way to write to a file by rewriting the lines except the ones to delete. But I want to know is there an efficient way to delete or update a line in place or append at the last in a file using file pointers in Python.
python python-3.x file-io file-handling
python python-3.x file-io file-handling
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
asked Mar 23 at 3:21
Paras KarnawatParas Karnawat
13
13
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Appending to the end is easy:
with open('somefile', 'a') as f:
f.write(line) # Or with print to add a newline for you, print(line, file=f)
In the middle, you're generally stuck; unless the new line is exactly the same length as the existing line, you'll have to move all the data after that line around to make it work, and that risks data corruption if anything (including non-software issues like a power outage) goes wrong. In that case, just write a new file, and use os.replace to atomically replace the old file with the new file after the new file is written out completely.
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
I want to know if there's a way to delete a line without rewriting the whole file except that line.
– Paras Karnawat
Mar 23 at 3:29
@ParasKarnawat: Unless the line is at the end of the file, you're going to have to rewrite every byte from that line onward. And as I said, doing so in a crash-safe way is effectively impossible (barring file system transactional write APIs, which Python doesn't give you access to even if they exist), so rewriting is the only way to do this safely.
– ShadowRanger
Mar 23 at 3:39
Alright, thanks a lot!
– Paras Karnawat
Mar 23 at 3:41
@ParasKarnawat: There are solutions that work for replacing lines at the end of a file, where at least you're not stuck with a massive copy down operation, but even there you risk data corruption if you're interrupted in the middle.
– ShadowRanger
Mar 23 at 3:43
Can you explain that way, I just want to try it and implement it to see how it works?
– Paras Karnawat
Mar 23 at 3:44
|
show 2 more comments
Your Answer
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Appending to the end is easy:
with open('somefile', 'a') as f:
f.write(line) # Or with print to add a newline for you, print(line, file=f)
In the middle, you're generally stuck; unless the new line is exactly the same length as the existing line, you'll have to move all the data after that line around to make it work, and that risks data corruption if anything (including non-software issues like a power outage) goes wrong. In that case, just write a new file, and use os.replace to atomically replace the old file with the new file after the new file is written out completely.
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
I want to know if there's a way to delete a line without rewriting the whole file except that line.
– Paras Karnawat
Mar 23 at 3:29
@ParasKarnawat: Unless the line is at the end of the file, you're going to have to rewrite every byte from that line onward. And as I said, doing so in a crash-safe way is effectively impossible (barring file system transactional write APIs, which Python doesn't give you access to even if they exist), so rewriting is the only way to do this safely.
– ShadowRanger
Mar 23 at 3:39
Alright, thanks a lot!
– Paras Karnawat
Mar 23 at 3:41
@ParasKarnawat: There are solutions that work for replacing lines at the end of a file, where at least you're not stuck with a massive copy down operation, but even there you risk data corruption if you're interrupted in the middle.
– ShadowRanger
Mar 23 at 3:43
Can you explain that way, I just want to try it and implement it to see how it works?
– Paras Karnawat
Mar 23 at 3:44
|
show 2 more comments
Appending to the end is easy:
with open('somefile', 'a') as f:
f.write(line) # Or with print to add a newline for you, print(line, file=f)
In the middle, you're generally stuck; unless the new line is exactly the same length as the existing line, you'll have to move all the data after that line around to make it work, and that risks data corruption if anything (including non-software issues like a power outage) goes wrong. In that case, just write a new file, and use os.replace to atomically replace the old file with the new file after the new file is written out completely.
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
I want to know if there's a way to delete a line without rewriting the whole file except that line.
– Paras Karnawat
Mar 23 at 3:29
@ParasKarnawat: Unless the line is at the end of the file, you're going to have to rewrite every byte from that line onward. And as I said, doing so in a crash-safe way is effectively impossible (barring file system transactional write APIs, which Python doesn't give you access to even if they exist), so rewriting is the only way to do this safely.
– ShadowRanger
Mar 23 at 3:39
Alright, thanks a lot!
– Paras Karnawat
Mar 23 at 3:41
@ParasKarnawat: There are solutions that work for replacing lines at the end of a file, where at least you're not stuck with a massive copy down operation, but even there you risk data corruption if you're interrupted in the middle.
– ShadowRanger
Mar 23 at 3:43
Can you explain that way, I just want to try it and implement it to see how it works?
– Paras Karnawat
Mar 23 at 3:44
|
show 2 more comments
Appending to the end is easy:
with open('somefile', 'a') as f:
f.write(line) # Or with print to add a newline for you, print(line, file=f)
In the middle, you're generally stuck; unless the new line is exactly the same length as the existing line, you'll have to move all the data after that line around to make it work, and that risks data corruption if anything (including non-software issues like a power outage) goes wrong. In that case, just write a new file, and use os.replace to atomically replace the old file with the new file after the new file is written out completely.
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
Appending to the end is easy:
with open('somefile', 'a') as f:
f.write(line) # Or with print to add a newline for you, print(line, file=f)
In the middle, you're generally stuck; unless the new line is exactly the same length as the existing line, you'll have to move all the data after that line around to make it work, and that risks data corruption if anything (including non-software issues like a power outage) goes wrong. In that case, just write a new file, and use os.replace to atomically replace the old file with the new file after the new file is written out completely.
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
answered Mar 23 at 3:28
ShadowRangerShadowRanger
65.2k664103
65.2k664103
I want to know if there's a way to delete a line without rewriting the whole file except that line.
– Paras Karnawat
Mar 23 at 3:29
@ParasKarnawat: Unless the line is at the end of the file, you're going to have to rewrite every byte from that line onward. And as I said, doing so in a crash-safe way is effectively impossible (barring file system transactional write APIs, which Python doesn't give you access to even if they exist), so rewriting is the only way to do this safely.
– ShadowRanger
Mar 23 at 3:39
Alright, thanks a lot!
– Paras Karnawat
Mar 23 at 3:41
@ParasKarnawat: There are solutions that work for replacing lines at the end of a file, where at least you're not stuck with a massive copy down operation, but even there you risk data corruption if you're interrupted in the middle.
– ShadowRanger
Mar 23 at 3:43
Can you explain that way, I just want to try it and implement it to see how it works?
– Paras Karnawat
Mar 23 at 3:44
|
show 2 more comments
I want to know if there's a way to delete a line without rewriting the whole file except that line.
– Paras Karnawat
Mar 23 at 3:29
@ParasKarnawat: Unless the line is at the end of the file, you're going to have to rewrite every byte from that line onward. And as I said, doing so in a crash-safe way is effectively impossible (barring file system transactional write APIs, which Python doesn't give you access to even if they exist), so rewriting is the only way to do this safely.
– ShadowRanger
Mar 23 at 3:39
Alright, thanks a lot!
– Paras Karnawat
Mar 23 at 3:41
@ParasKarnawat: There are solutions that work for replacing lines at the end of a file, where at least you're not stuck with a massive copy down operation, but even there you risk data corruption if you're interrupted in the middle.
– ShadowRanger
Mar 23 at 3:43
Can you explain that way, I just want to try it and implement it to see how it works?
– Paras Karnawat
Mar 23 at 3:44
I want to know if there's a way to delete a line without rewriting the whole file except that line.
– Paras Karnawat
Mar 23 at 3:29
I want to know if there's a way to delete a line without rewriting the whole file except that line.
– Paras Karnawat
Mar 23 at 3:29
@ParasKarnawat: Unless the line is at the end of the file, you're going to have to rewrite every byte from that line onward. And as I said, doing so in a crash-safe way is effectively impossible (barring file system transactional write APIs, which Python doesn't give you access to even if they exist), so rewriting is the only way to do this safely.
– ShadowRanger
Mar 23 at 3:39
@ParasKarnawat: Unless the line is at the end of the file, you're going to have to rewrite every byte from that line onward. And as I said, doing so in a crash-safe way is effectively impossible (barring file system transactional write APIs, which Python doesn't give you access to even if they exist), so rewriting is the only way to do this safely.
– ShadowRanger
Mar 23 at 3:39
Alright, thanks a lot!
– Paras Karnawat
Mar 23 at 3:41
Alright, thanks a lot!
– Paras Karnawat
Mar 23 at 3:41
@ParasKarnawat: There are solutions that work for replacing lines at the end of a file, where at least you're not stuck with a massive copy down operation, but even there you risk data corruption if you're interrupted in the middle.
– ShadowRanger
Mar 23 at 3:43
@ParasKarnawat: There are solutions that work for replacing lines at the end of a file, where at least you're not stuck with a massive copy down operation, but even there you risk data corruption if you're interrupted in the middle.
– ShadowRanger
Mar 23 at 3:43
Can you explain that way, I just want to try it and implement it to see how it works?
– Paras Karnawat
Mar 23 at 3:44
Can you explain that way, I just want to try it and implement it to see how it works?
– Paras Karnawat
Mar 23 at 3:44
|
show 2 more comments
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