Introducing Python's map Function
Tags: python
Published: 2020-02-27 21:53:04

# Mapping Function

Hey there! Let’s talk about code and how repetitive it can get. Writing repeated code never looks good to developers. However, sometimes it's hard to avoid. Knowing this, there are tools made to help us shorten code. The tool I'm discussing is the `map` function. The `map` function allows you to iterate through a list applying the desired function to each item of the list. Let's break down exactly how this works.

The code snippet below represents a function that takes a number and adds one to it. Given a list of numbers, how can I apply the `add_number` function to each element in the iterable?

```python
def add_number(number):
    return number + 1
```

Using the `map` function, you will pass in the desired function and list as arguments. The given function will then be used over each list item.

```python
def add_number(number):
    return number + 1

numbers = [1, 2, 3]

mapped_numbers = map(add_number, numbers)

print("After Adding 1")
for number in mapped_numbers:
    print(number)

names = ["Guido", "John", "Derek"]

print("Lengths of names")
for name_length in map(len, names):
    print(name_length)
```

**Output:**

```
After Adding 1
2
3
4
Lengths of names
5
4
5
```

The `map` function can make long steps, really short. The goal here is to reduce repetitive code. With `map`, it can be achieved. Now our code can be clean, concise and presentable!

## Example

Here's the longer way to reach the goal of this program:

```python

# The function below removes all vowels from the word provided in the argument
def no_vowel(word):
    for ch in "AEIOU":
        word = word.replace(ch, "")
        word = word.replace(ch.lower(), "")
    return word


# We want to remove each vowel from each word in the list below
word_list = ["Captain", "Crunch", "Cereal", "Yummy"]

# With each removed vowel we want to append the new word into the list below
removed_vowel_list = []

for word in word_list:
    removed_vowels = no_vowel(word)
    removed_vowel_list.append(removed_vowels)

string = f"{word_list} --> {removed_vowel_list}"

print(string)

```

### Output

```python
    ['Captain', 'Crunch', 'Cereal', 'Yummy'] --> ['Cptn', 'Crnch', 'Crl', 'Ymmy']
```

But when using the map() function, here's how the code can be shortened:

```python
    def no_vowel(word):
        for ch in "AEIOU":
            word = word.replace(ch, "")
            word = word.replace(ch.lower(), "")
        return word

    word_list = ["Captain", "Crunch", "Cereal", "Yummy"]

    new_list = list(map(no_vowel, word_list))

    string = f'{word_list} --> {new_list}'

    print(string)
```

### Output

```python
    ['Captain', 'Crunch', 'Cereal', 'Yummy'] --> ['Cptn', 'Crnch', 'Crl', 'Ymmy']
```

# Extra Information on Map

When using `map`, it's good to know that it is a type of generator. The return value for `map` is a map object(iterator). Think of it as a list but it can't store data. `Map` is a lazy generator, meaning it's single use and only evaluates when necessary. Calling a function on map can allow it to be used.


```python
nums = [10, 5, 13, 7]

mapped = map(print, nums) # nothing gets printed

list(mapped) # things get printed (caling function on map)

list(mapped) # nothing gets printed (single use)
```

For more information on `map` you can follow the documentation. https://docs.python.org/3/library/functions.html#map