Checking var is a number?

[dav.phillips]

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]

da**********@ntlworld.com írta:

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.
There are different types of number in Python.

Integers and Long integers (type: 'int', 'long')
Decimal numbers (class 'decimal.Decimal')
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:

....

print_type(12) this is an integer print_type(12L) this is a long integer print_type(3.5) this is a float print_type('hello world') this is something else... print_type('44') this is something else... d = Decimal('123')
print_type(d) this is a decimal The project i have been given to work in is all CGI written
in Python.

Probaby you wanted to convert a string into a number? For example:
int(s) 1234 s = 'Foo'
int(s) Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: invalid literal for int(): Foo
Or you can catch the exception:
s = 'Foo2'
try: .... intval = int(s)
.... except ValueError:
.... print "This cannot be converted to an int."
....
This cannot be converted to an int.

Good luck!

Laszlo

[Fredrik Lundh]

da**********@ntlworld.com wrote:

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.
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.
Also can anyone recommend a reference book apart from dive into python
preferably a reference with good examples of how to impliment code.

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/

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[dav.phillips]

> Good luck!

Laszlo

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

Cheers
David P

[dav.phillips]

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]

da**********@ntlworld.com wrote:

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.

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

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