Problems with user input

[Steven Bethard]

Florian Wilhelm <Florian.Wilhelm <at> web.de> writes:
> 
> import sys
> 
> print "Input: (y/N) ",
> input = sys.stdin.read(1)
> print "Hello World"
> print "Your input:", input
> 
> produces this output...
> 
> Input: (y/N) y
>  Hello World
> Your input: y
> 
> Can somebody explain why the whitespace char appears
> in front of "Hello World"???

This is the behavior of the print statement.  For example:

>>> print "X", sys.stdin.read(1), "Y"
X1
 1 Y

Every comma between two expressions in the print statement adds a space.  As you
can see from the code above, the space isn't inserted until after the following
expression (sys.stdin.read(1)) is executed, and hence I get the space from the
print statement following the newline I inserted when I pressed <ENTER> after
typing 1.

If instead, you use sys.stdout.write, you get:

>>> def f():
...     sys.stdout.write("X%s" % sys.stdin.read(1))
...     sys.stdout.write("Y\n")
...
>>> f()
1
X1Y

sys.stdout.write doesn't insert spaces (unless you put spaces in the strings). 
In general, if you want a particular format, you should use sys.stdout.write
instead of print, since the print statement has a number of such idiosyncracies.

Steve