I'm trying to insert some text at specific position of file using this:
with open("test.txt","r+") as f: f.seek(5) f.write("B") But this overwrites character at position 5 with new data ("B") instead of inserting it.
for example if i have
AAAAAAAAAA in file test.txt and run the code I get AAAAABAAAA instead of AAAAABAAAAA (five A must be after B)
How can i insert at desired position of file instead of overwrite?
There are three answers for that:
open for the python). Moreover, as I checked (Sep 2018) a fallocate module on pypi does not support it, so you need to write a low-level code to do FALLOC_FL_INSERT_RANGE ioctl.TL;DR; If you file is small, read it into memory and do insert in memory. If you file is medium size (1-2Gb) do it in temp file and rename it after that. If your file is large, use windowed operations or dig down to FALLOC_FL_INSERT_RANGE (if you have a relatively modern linux).
This worked for me :
with open("test.txt","r+") as f: f.seek(5) #first fseek to the position line=f.readline() #read everything after it f.seek(5) #since file pointer has moved, fseek back to 5 f.write("B") #write the letter f.write(line) #write the remaining part Original : AAAAAAAAAA After : AAAAABAAAAA 
f1 = open("test.txt","r+") f1.seek(5) data = "{}{}".format("B",f1.readline()) f1.seek(5) f1.write(data) f1.close() 
