What is the perfect counterpart in Python for while not EOF

Question

To read some text file  in C or Pascal  I always use the following snippets to read the data until EOF   while not eof do begin   readline a     do something  end    Thus  I wonder how can I do this simple and fast in Python

User · Answer

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   lt string gt    line 1  in  lt module gt   EOFError  EOF when reading a line   Or press Ctrl-Z at a raw input   prompt  Windows  Ctrl-Z Linux

User · Answer

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

User · Answer

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    amp  amp   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

User · Answer

Loop over the file to read lines   with open  somefile   as openfileobject      for line in openfileobject          do something     File objects are iterable and yield lines until EOF  Using the file object as an iterable uses  a buffer to ensure performant reads   You can do the same with the stdin  no need to use raw input     import sys  for line in sys stdin      do something     To complete the picture  binary reads can be done with   from functools import partial  with open  somefile    rb   as openfileobject      for chunk in iter partial openfileobject read  1024   b             do something     where chunk will contain up to 1024 bytes at a time from the file  and iteration stops when openfileobject read 1024  starts returning empty byte strings

User · Answer

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

User · Answer

You can use the following code snippet   readlines   reads in the whole file at once and splits it by line   line   obj readlines

User · Answer

In addition to  dawg s great answer  the equivalent solution using walrus operator  Python  gt   3 8   with open filename   rb   as f      while buf    f read max size           process buf

[python] What is the perfect counterpart in Python for "while not EOF"

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