Checking var is a number?

[dav.phillips@ntlworld.com]

Hi,
I am very new to all this and need to know how to check
a variable to see if it is a number or not. Also can anyone
recommend a reference book apart from dive into python
preferably a reference with good examples of how to impliment
code.

The project i have been given to work in is all CGI written
in Python.

Many Thanks
David Phillips

[Laszlo Nagy]

Re: Checking var is a number?

dav.phillips@nt lworld.com írta:[color=blue]
> Hi,
> I am very new to all this and need to know how to check
> a variable to see if it is a number or not. Also can anyone
> recommend a reference book apart from dive into python
> preferably a reference with good examples of how to impliment
> code.
>[/color]
There are different types of number in Python.

Integers and Long integers (type: 'int', 'long')
Decimal numbers (class 'decimal.Decima l')
Floating point numbers (type 'float')

You can check this way:

import decimal

def print_type(var) :
if isinstance(var, int):
print "this is an integer"
elif isinstance(var, long):
print "this is a long integer"
elif isinstance(var, decimal.Decimal ):
print "this is a decimal"
elif isinstance(var, float):
print "this is a float"
else:
print "this is something else..."

Test this:

....[color=blue][color=green][color=darkred]
>>> print_type(12)[/color][/color][/color]
this is an integer[color=blue][color=green][color=darkred]
>>> print_type(12L)[/color][/color][/color]
this is a long integer[color=blue][color=green][color=darkred]
>>> print_type(3.5)[/color][/color][/color]
this is a float[color=blue][color=green][color=darkred]
>>> print_type('hel lo world')[/color][/color][/color]
this is something else...[color=blue][color=green][color=darkred]
>>> print_type('44' )[/color][/color][/color]
this is something else...[color=blue][color=green][color=darkred]
>>> d = Decimal('123')
>>> print_type(d)[/color][/color][/color]
this is a decimal[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]
[color=blue]
> The project i have been given to work in is all CGI written
> in Python.
>[/color]
Probaby you wanted to convert a string into a number? For example:
[color=blue][color=green][color=darkred]
>>> int(s)[/color][/color][/color]
1234[color=blue][color=green][color=darkred]
>>> s = 'Foo'
>>> int(s)[/color][/color][/color]
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: invalid literal for int(): Foo[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Or you can catch the exception:
[color=blue][color=green][color=darkred]
>>> s = 'Foo2'
>>> try:[/color][/color][/color]
.... intval = int(s)
.... except ValueError:
.... print "This cannot be converted to an int."
....
This cannot be converted to an int.[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Good luck!

Laszlo

[Fredrik Lundh]

Re: Checking var is a number?

dav.phillips@nt lworld.com wrote:
[color=blue]
> I am very new to all this and need to know how to check
> a variable to see if it is a number or not.[/color]

assuming that "variable" means "string object" and "number" means
"integer", you can use the isdigit predicate:

if var.isdigit():
print "all characters in", var, "are digits"

if you want to check for anything that can be converted to a float, the
best way is to do the conversion and trap any ValueError that may occur:

try:
value = float(var)
except ValueError:
print "not a valid float"

if you want an integer instead, replace "float" with "int".

if you had something else in mind, let us know.
[color=blue]
> Also can anyone recommend a reference book apart from dive into python
> preferably a reference with good examples of how to impliment code.[/color]

you can find an extensive list of available books here:

http://wiki.python.org/moin/PythonBooks

some on-line code collections:

http://aspn.activestate.com/ASPN/Python/Cookbook/

http://effbot.org/zone/librarybook-index.htm

and don't forget the core references:

http://docs.python.org/lib/

http://docs.python.org/ref/

</F>

[dav.phillips@ntlworld.com]

Re: Checking var is a number?

> Good luck![color=blue]
> Laszlo[/color]

I actually managed to get it sorted but i like that way of
doing it much better actually :)

Cheers
David P

[dav.phillips@ntlworld.com]

Re: Checking var is a number?

I took a variable to mean a container for diffirent kinds of
information
either strings or integers etc, as i am mainly a asp, php, asp.net
developer.

Thanks for the list of references, that will come in very handy

Cheers Guys
David P

[Fredrik Lundh]

Re: Checking var is a number?

dav.phillips@nt lworld.com wrote:
[color=blue]
> I took a variable to mean a container for diffirent kinds of
> information either strings or integers etc, as i am mainly a
> asp, php, asp.net developer.[/color]

in python, a variable is a name that refers to a specific object. it's
the object that has a type and a value, not the variable. this article
might be somewhat helpful:

http://effbot.org/zone/python-objects.htm

</F>