python variables, classes

Question

Dear All, Trying to learn python, classes, and how to pass variables between. Going through a learning guide here, and am having trouble with the following Error:

TypeError: unbound method scan() must be called with lexicon instance as first argument (got str instance instead)

Can someone please help me understand this better? THANKS!!!

class lexicon (object):
 def __init__(self,data):
 self.direction = data
 self.words = data.split()
 def scan(self):
 return self.words
def main():
 stuff = raw_input('> ') 
 x = lexicon.scan(stuff)
if __name__ == '__main__':
 main()

Answer 1

You have to instantiate an object of type lexicon before you can invoke one of its methods. i.e.

lex = lexicon(data)
lex.scan()

• Mike Ramirez: good reading to understand bound vs unbound methods. docs.python.org/reference/datamodel.html and docs.python.org/library/stdtypes.html#methods
• Cmag: Thanks guys! Would it be appropriate to explain the word 'instantiate' as 'define'? In other words... You must define the class and functions within that class before you can use them...
• Mike Ramirez: @Clustermagnet No. Because a class does not need to be 'instaniated' to run it's methods, if they are static or class methods. Instaniated would be best described as creating the object in memory. static methods and class methods exist as part of the class but the class does not need to be instinated to use them.

Answer 2

In addition to what Jim said, self is automatically passed in for you. (And it's not required to be called self but calling it something else will just confuse yourself and other people)