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Map Function in Python

Today I discovered the map function in Python. Map causes some simple for loops to be verbose and unnecessary. Let's look at how to change a list of integers to a list of strings. First we'll use a for loop:

>>> list = [1, 2, 3, 4, 5]
>>> index = 0
>>> for x in list:
...   list[index] = str(list[index])
...   index += 1
...
>>> print list
['1', '2', '3', '4', '5']

Now we'll use the map function and we'll define our 1-5 list using the range function

>>> list1 = range(1, 6)
>>> map(str, list1)        # performs str to each index of list1
['1', '2', '3', '4', '5']

You can also make your list within the map function, such as splitting a string into a list. The following example shows how you can define a method using else, elif (else if), and if statements, then run your method to a single string with the map function, resulting in a list with the method performed to each index.

>>> def pluralize(word):
...   if word[-1] == 'y':
...     return word[:len(word) - 1] + 'ies'      # replaces y with ies
...   elif word[-1] == 's':
...     return word + 'es'
...   else:
...     return word + 's'
...
>>> map( pluralize, "The sexy waitress brought me a beer".split())
['Thes', 'sexies', 'waitresses', 'broughts', 'mes', 'as', 'beers']
>>># my husband chose the sentence

I simplified my method to not account for every scenario put into it. Although this specific example does not produce correct English, the map function correctly split the string on the whitespace and carried out the method on each index of the list.

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