You can use below code snippet to read line by line, till end of file
line = obj.readline()
while(line != ''):
# Do Something
line = obj.readline()
While there are suggestions above for "doing it the python way", if one wants to really have a logic based on EOF, then I suppose using exception handling is the way to do it --
try:
line = raw_input()
... whatever needs to be done incase of no EOF ...
except EOFError:
... whatever needs to be done incase of EOF ...
Example:
$ echo test | python -c "while True: print raw_input()"
test
Traceback (most recent call last):
File "<string>", line 1, in <module>
EOFError: EOF when reading a line
Or press Ctrl-Z at a raw_input()
prompt (Windows, Ctrl-Z Linux)
The Python idiom for opening a file and reading it line-by-line is:
with open('filename') as f:
for line in f:
do_something(line)
The file will be automatically closed at the end of the above code (the with
construct takes care of that).
Finally, it is worth noting that line
will preserve the trailing newline. This can be easily removed using:
line = line.rstrip()
You can use the following code snippet. readlines() reads in the whole file at once and splits it by line.
line = obj.readlines()
You can imitate the C idiom in Python.
To read a buffer up to max_size
number of bytes, you can do this:
with open(filename, 'rb') as f:
while True:
buf = f.read(max_size)
if not buf:
break
process(buf)
Or, a text file line by line:
# warning -- not idiomatic Python! See below...
with open(filename, 'rb') as f:
while True:
line = f.readline()
if not line:
break
process(line)
You need to use while True / break
construct since there is no eof test in Python other than the lack of bytes returned from a read.
In C, you might have:
while ((ch != '\n') && (ch != EOF)) {
// read the next ch and add to a buffer
// ..
}
However, you cannot have this in Python:
while (line = f.readline()):
# syntax error
because assignments are not allowed in expressions in Python (although recent versions of Python can mimic this using assignment expressions, see below).
It is certainly more idiomatic in Python to do this:
# THIS IS IDIOMATIC Python. Do this:
with open('somefile') as f:
for line in f:
process(line)
Update: Since Python 3.8 you may also use assignment expressions:
while line := f.readline():
process(line)
In addition to @dawg's great answer, the equivalent solution using walrus operator (Python >= 3.8):
with open(filename, 'rb') as f:
while buf := f.read(max_size):
process(buf)
Source: Stackoverflow.com