[Tutor] Why different behaviours?

[Danny Yoo]

On Fri, 26 Oct 2001, Danny Kohn wrote:

> Why does:
> import string, sys
> f=open('d:/Dokument/Programprojekt/pythonworks/projects/H2/Lexicon.txt', 'r')
> line = f.readline()
> print line
> 
> and:
> 
> import string, sys
> f=open('d:/Dokument/Programprojekt/pythonworks/projects/H2/Lexicon.txt', 'r')
> for line in f.readline():
> 	print line


The variable naming in your second version might be obscuring an issue:

> for line in f.readline():
> 	print line

In this case, we're asking Python to do a for loop along every thing in an
f.readline().  In that case, we're going to go along every character of
that read line, so the loop might be better written as:

##
for character in f.readline():
    print line
###


Also, Python's "print" statement will automatically put a newline, unless
we place a trailing comma.  We can see this from this interpreter session:

###
>>> print "abc"
abc
>>> for letter in "abc":
...     print letter
...
a
b
c
>>> for letter in "abc":
...     print letter,
...
a b c
###


It sounds like you've had some programming experience already, so I don't
have qualms about recommending the official Python library:

    http://www.python.org/doc/current/tut/tut.html

The section on "Fancier Output Formatting" should give you more control
over how your programs print things.


> Also, what would be the way to read line after line until end of file.
> How to detect end of file when reading a sequential file this way?

According to:

http://www.python.org/doc/current/tut/node9.html#SECTION009200000000000000000

"""f.readline() reads a single line from the file; a newline character
(\n) is left at the end of the string, and is only omitted on the last
line of the file if the file doesn't end in a newline. This makes the
return value unambiguous; if f.readline() returns an empty string, the end
of the file has been reached, while a blank line is represented by '\n', a
string containing only a single newline."""


If you have more questions, please feel free to ask.  Good luck!