Re: Does a function like isset() exist in Python?
In article <[EMAIL PROTECTED]>, Patrick Fitzsimmons <[EMAIL PROTECTED]> wrote: > Hi, > > I'm sure I should know this, but I can't find it in the manual. > > Is there a function in Python like the function in PHP isset()? It > should take a variable name and return True or False depending on > whether the variable is initialized. > > Thanks for any help, > Patrick The straight-forward thing would be to simply access the variable and catch any resulting NameError exception that's raised if it's not defined: try: x print "x is defined" except NameError: print "no it's not" Next question, why do you want to do this? I suspect for most idioms where you would something like this, the more pythonic way would be to set the variable to None at some point, then test to see if it's still None later on: x = None while foo: if blah: x = baz if x != None: print "x was assigned a value" -- http://mail.python.org/mailman/listinfo/python-list
Re: Does a function like isset() exist in Python?
On Wed, 22 Jun 2005 23:09:57 -0400, Patrick Fitzsimmons wrote: > Hi, > > I'm sure I should know this, but I can't find it in the manual. > > Is there a function in Python like the function in PHP isset()? It > should take a variable name and return True or False depending on > whether the variable is initialized. What would you use such a function for? The closest thing I can think of is testing whether a particular object exists. Eg to test whether your program is running under a version of Python that defines bools, and if not, define your own objects which act in a similar way, you would say try: False except NameError: False = 0 True = not False Note that there is no need to do something with the name "False" in the try clause -- just use it. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: Does a function like isset() exist in Python?
George Sakkis wrote: > There are no unitialized variables in python; if you try to access an > undefined name, a NameError exception is raised: > > try: > print "foo is", foo > except NameError: > print "foo is undefined" note the order of evaluation: >>> try: ... print "foo is", foo ... except NameError: ... print "foo is undefined" ... foo is foo is undefined >>> -- http://mail.python.org/mailman/listinfo/python-list
Re: Does a function like isset() exist in Python?
"Patrick Fitzsimmons" wrote: > Hi, > > I'm sure I should know this, but I can't find it in the manual. > > Is there a function in Python like the function in PHP isset()? It > should take a variable name and return True or False depending on > whether the variable is initialized. > > Thanks for any help, > Patrick There are no unitialized variables in python; if you try to access an undefined name, a NameError exception is raised: try: print "foo is", foo except NameError: print "foo is undefined" To undefine a defined name, use del: >>> foo=None >>> print foo None >>> del foo >>> print foo NameError: name 'foo' is not defined George -- http://mail.python.org/mailman/listinfo/python-list
Re: Does a function like isset() exist in Python?
Patrick Fitzsimmons wrote: > Hi, > > I'm sure I should know this, but I can't find it in the manual. > > Is there a function in Python like the function in PHP isset()? It > should take a variable name and return True or False depending on > whether the variable is initialized. > > Thanks for any help, > Patrick try: doDomething(myVar) except NameError: print "myVar is not set" /Esben -- http://mail.python.org/mailman/listinfo/python-list
Re: Does a function like isset() exist in Python?
I'm not sure what you mean by initialized. If you're asking if the identifier exists in the namespace, then you can use hasattr(), or simply try to reference it and catch the exception if it doesn't exist. If the identifier exists, it always has a value. On the other hand, there is a small gotcha on identifiers in functions/methods where they have to have a value assigned before you can reference them. If you run into this at all frequently, you're probably making your methods too big to be easily understood. Of course, if you're playing games with the stack and trying to print out the values of identifiers on the calling chain on an exception, all bets are off. See the code in the py.test module (part of the PyPy project) for how you can do this. John Roth "Patrick Fitzsimmons" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] Hi, I'm sure I should know this, but I can't find it in the manual. Is there a function in Python like the function in PHP isset()? It should take a variable name and return True or False depending on whether the variable is initialized. Thanks for any help, Patrick -- http://mail.python.org/mailman/listinfo/python-list
Re: Does a function like isset() exist in Python?
On 6/23/05, Patrick Fitzsimmons <[EMAIL PROTECTED]> wrote: > Hi, > > I'm sure I should know this, but I can't find it in the manual. > > Is there a function in Python like the function in PHP isset()? It > should take a variable name and return True or False depending on > whether the variable is initialized. There's no direct function to acheive this however you can find out the answer by looking in locals() and globals() dictionaries. Before doing this though you should consider why you want to do it. A lot of this time when this kind of thing comes up the problem can better be solved by rearranging the code such that you don't need to check isset() in the first place. Tim > > Thanks for any help, > Patrick > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
Does a function like isset() exist in Python?
Hi, I'm sure I should know this, but I can't find it in the manual. Is there a function in Python like the function in PHP isset()? It should take a variable name and return True or False depending on whether the variable is initialized. Thanks for any help, Patrick -- http://mail.python.org/mailman/listinfo/python-list
