Python f.read not reading the correct number of bytes -

i have code supposed read 4 bytes reading 3 sometimes:

f = open('test.sgy', 'r+') f.seek(99716) aaa = f.read(4) bbb = f.read(4) ccc = f.read(4) print len(aaa) print len(bbb) print len(ccc)  exit() 

and program returns: 4 3 4

what doing wrong? thanks!

you're assuming read not. documentation tells you:

read(...)     read([size]) -> read @ size bytes, returned string. 

it reads at most size bytes

if need exactly size bytes, you'll have create wrapper function.

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here's (not thoroughly tested) example can adapt:

def read_exactly( fd, size ):     data=""     remaining= size     while remaining>0:      #or "while remaining", if you'd         newdata= fd.read(remaining)         if len(newdata)==0: #problem             raise ioerror("failed read enough data")         data+=newdata         remaining-= len(newdata)     return data 

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as mark dickinson mentioned in comments, if you're on windows, make sure you're reading in binary mode - otherwise risk reading (binary) data wrong.