__getslice__ how do you call it in the function

Question

I have a class Sentence with a magic method function __getslice__

I am not understanding how to call that function ?

I am trying to do slicing of words. so for example if the string is "HELLO WORLD, james" , and I slice it at [0:1] , I expect to get "HELLO"

I am getting instead this error: 'method' object is not subscriptable

Here is my code:

    class Sentence:
        def __init__(self, string):
            self._string = string
        def getSentence(self):
            return self._string
        def getWords(self):
            return self._string.split()
        def getLength(self):
            return len(self._string)
        def getNumWords(self):
            return len(self._string.split())
        def capitalize(self):
            self._string =  self._string.upper()
        def punctation(self):
            self._string = self._string + ", "
        def __str__(self):
            return self._string
        def __getitem__(self, k):
            return self._string[k]
        def __len__(self):
            return self._String
        def __getslice__(self, start, end):
            return self[max(0, start):max(0, end):]
        def __add__(self, other):
            self._string = self._string + other
            return self._string
        def __frequencyTable__(self, word):
            count = 0
            for w in self._string:
                if self._string.has_key(word):
                    count = count + 1
            return count
        def __contains__(self, word):
            return word in self._string


def functionTesting():
    hippo = Sentence("hello world")
    print(hippo.getSentence())
    print(hippo.getLength())
    print(hippo.getNumWords())
    print(hippo.getWords())

    hippo.capitalize()
    hippo.punctation()

    print(hippo.getSentence())

    print("HELLO" in hippo)           ##contains

    print(hippo.__getitem__(0))      ##__getitem

    print(hippo.__add__("james"))      ##__add__

    print(hippo.__getslice__[0:1])



functionTesting()

Also where can I learn more about magic method functions ? As it seems I am having trouble calling the functions more than writing them

Answer 1

When you do hippo.__getslice__[0:1] you are actually trying to slice the method hippo.__getslice__. That is why it is failing with the error

'method' object is not subscriptable

Important Note: __getslice__ is deprecated since Python 2.0 and it is not available in Python 3.x. Quoting the official documentation of __getslice__,

Deprecated since version 2.0: Support slice objects as parameters to the __getitem__() method. (However, built-in types in CPython currently still implement __getslice__(). Therefore, you have to override it in derived classes when implementing slicing.)

So you should use __getitem__ for slicing. Quoting the question,

for example if the string is "HELLO WORLD, james" , and I slice it at [0:1] , I expect to get "HELLO"

Since you want to get words with slicing, if the key passed to __getitem__ is a slice object, then call self.getWords() and slice the returned object like shown below

def __getitem__(self, k):
    if isinstance(k, slice):
        return self.getWords()[k]
    return self._string[k]

....
print(hippo[0:1])
['HELLO']

Note 1: You don't have to explicitly call __getitem__ when you are subscripting the hippo object. You can simply do

print(hippo[0])
# H

This will internally call __getitem__ with k as 0.

Note 2: Same as the previous one. You don't have to explicitly call __add__ and that can be implicitly called with the arithmetic operator +, like this

print(hippo + "james")
# HELLO WORLD, james

Note 3: In your __frequenceTable__ implementation, you are using has_key method (which is a deprecated dictionary method on a string. So, at runtime, your program will fail with

AttributeError: 'str' object has no attribute 'has_key'

Perhaps you meant to use in operator.

def __frequencyTable__(self, word):
    count = 0
    for w in self._string:
        if word in self._string:
            count = count + 1
    return count

PS: I am not sure what this __frequencyTable__ method tries to achieve.