Python 101 (part 6): Hedgehogs, Pythons And Funky Chameleons - Enter The Funky Chameleon

(Page 8 of 10 )

The order in which arguments are passed to a function is important - the following example assumes that the name is passed as the first argument, and the age as the second.

>>> def User(name, age):
...     print "Hello, " + name + ". How strange that we are both " + age +
" years old."
...
>>> User("Funky Chameleon", "23")
Hello, Funky Chameleon. How strange that we are both 23 years old.
>>>

If you get the order wrong, you may get unexpected results.

>>> User("23", "Funky Chameleon")
Hello, 23. How strange that we are both Funky Chameleon years old.
>>>

However, it's possible to override this behaviour in the function call itself, by specifying the arguments as name-value pairs.

>>> User(age="23", name="Funky Chameleon")
Hello, Funky Chameleon. How strange that we are both 23 years old.
>>>

Additionally, you can specify certain arguments to be optional, by setting default values for them in the function definition. Consider the following example, which requires two arguments, a URL and a language to display it in. If the language argument is omitted, a default value is used.

>>> def displayURL(url, lang="English"):
...     print "Displaying URL <" + url + "> in " + lang
...
>>> displayURL("http://www.melonfire.com", "Spanish")
Displaying URL  in Spanish
>>> displayURL("http://www.melonfire.com")
Displaying URL  in English
>>>

Note, however, that the list of optional arguments must follow, not precede, the list of required arguments in the function definition.

All these examples have one thing in common - the list of arguments is fixed. Look what happens if you pass an extra argument to the User() function above,

>>> User("Harry the Hedgehog", "2", "male")
Traceback (innermost last):
File "", line 1, in ?
TypeError: too many arguments; expected 2, got 3
>>>

or miss out on a parameter when calling the function.

>>> User("Harry the Hedgehog")
Traceback (innermost last):
File "", line 1, in ?
TypeError: not enough arguments; expected 2, got 1
>>>

To handle situations such as there, Python functions come with a built-in secret weapon - the *variable argument. Consider the following function definition:

>>> def User(name, age, *more):
...     print "Name:", name
...     print "Age:", age
...     for x in more:
...             print "Additional argument:", x
...

In this case, extra arguments passed to the function will be stored in the variable "more" as a tuple; these arguments can then be extracted and processed using standard tuple operators or methods.

>>> User("Harry the Hedgehog", "2", "male")
Name: Harry the Hedgehog
Age: 2
Additional argument: male
>>> User("Harry the Hedgehog", "2", "male", "angry", "lives next door")
Name: Harry the Hedgehog
Age: 2
Additional argument: male
Additional argument: angry
Additional argument: lives next door
>>>

Here's an example which demonstrates how this works.

>>> def Product(*numlist):
...     product = 1;
...     for x in numlist:
...             product = product * x
...     return product
...
>>>

In this case, you can call the Product() function with as many arguments as you like; the "for" loop will iterate through the "numlist" tuple and multiply each one by the previous result.

>>> Product(2, 3)
6
>>> Product(2)
2
>>> Product(2, 10, 10, 1)
200
>>> Product(2, 10, 10, 6326, 236237238923490234)
OverflowError: integer literal too large
>>>

Oh, well...

Next: Flavour Of The Month >>
 

More Python Articles
More By Vikram Vaswani, (c) Melonfire

Comments On: Python 101 (part 6): Hedgehogs, Pythons And Funky Chameleons

>>> Be the FIRST to comment on this article!