Please excuse my confusion here but I have read the documentation regarding the seek() function in python (after having to use it) and although it helped me I am still a bit confused on the actual meaning of what it does, any explanations are much appreciated, thank you.
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python
When you open a file, the system points to the beginning of the file. Any read or write you do will happen from the beginning. A seek()
operation moves that pointer to some other part of the file so you can read or write at that place.
So, if you want to read the whole file but skip the first 20 bytes, open the file, seek(20)
to move to where you want to start reading, then continue with reading the file.
Or say you want to read every 10th byte, you could write a loop that does seek(9, 1)
(moves 9 bytes forward relative to the current positions), read(1)
(reads one byte), repeat.
The seek
function expect's an offset in bytes.
So if you have a text file with the following content:
simple.txt
abc
You can jump 1 byte to skip over the first character as following:
fp = open('simple.txt', 'r')
fp.seek(1)
print fp.readline()
>>> bc
fp = open('afile.png', 'rb')
fp.seek(16)
print 'width: {0}'.format(struct.unpack('>i', fp.read(4))[0])
print 'height: ', struct.unpack('>i', fp.read(4))[0]
Note: Once you call
read
you are changing the position of the read-head, which act's likeseek
.
For strings, forget about using WHENCE: use f.seek(0) to position at beginning of file and f.seek(len(f)+1) to position at the end of file. Use open(file, "r+") to read/write anywhere in a file. If you use "a+" you'll only be able to write (append) at the end of the file regardless of where you position the cursor.
Source: Stackoverflow.com