question on input function

Chris Rebert clp2 at rebertia.com
Mon Jul 20 04:44:45 CEST 2009


On Sun, Jul 19, 2009 at 7:07 PM, Richel Satumbaga<rlsatumbaga at yahoo.com> wrote:
> I am just learning python then I encountered an certain point in terms of
> using the input function of python.
> the source code:
>                        eq = input("enter an equation:");
>                        print " the result is : ";
>
>
> the output seen in the command window:
>>>>
> enter an equation:[m*x+b for m in (0,10,1),for x in (1,11,1), for b in
> (2,12,1)]
>
> Traceback (most recent call last):
>   File "C:/Python26/try", line 1, in <module>
>     eq = input("enter an equation:");
>   File "<string>", line 1
>     [m*x+b for m in (0,10,1),for x in (1,11,1), for b in (2,12,1)]
>                                ^
> SyntaxError: invalid syntax
>
>                   Is there any other way to enter those? or it must be coded
> in the source code?
> If in source code is it like in matlab where one can type:
>
> x = [0:1:10];
>
> to define the range of x which is form 0 to 10 with the increment of  1.

First, commas between the "for"s are not permitted, which gives us:

[m*x+b for m in (0,10,1) for x in (1,11,1) for b in (2,12,1)]

However, in Python, (i, j, k) is just a tuple (MATLAB: 1D matrix) of
the items i, j, and k.
What you want is a range, which is understandably created using the
range() function.
A step of 1 and a start of 0 are the defaults, and the stop value is
always excluded, so the code becomes:

[m*x+b for m in range(11) for x in range(1,12) for b in range(2,13)]

Which should be what you want.

For further explanation of the range() function:
range(b) - the numbers from 0 to b-1 with a step of 1
range(a,b) - the numbers from a to b-1 with a step of 1
range(a,b,c) - the numbers from a to b-1 with a step of c

Hope that helps.

Cheers,
Chris
-- 
http://blog.rebertia.com



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