• Comprehension here does not mean “understanding”, more like comprehensive.
  • For example, we have the following: 
    myList = [1,2,3,4,5]
[2*item for item in myList]
  • The output for that would be: 
    [2, 4, 6, 8, 10]
  • item can be any variable name you want.
    • Make sure it is the same variable name used in the entire code block.
  • It allows you to iterate over the list you have.
  • List Comprehensions with Filters: 
    # Provides a list with members from 0 ~ 99
myList = list(range(100))
filteredList = [item for item in myList if item % 10 == 0]
  • % is the modulus operator. It in this case provides the remainder, after diving by the number on the right-hand side (in this case 10).
    • If the remainder in this case is equal to 0, then the statement is true.
  • You will then receive an output similar to: 
    [0, 10, 20, 30, 40, 50, 60, 70, 80, 90]
  • If you want to show all numbers that are either 1 or 2: 
    filteredList = [item for item in myList if item % 10 < 3]
filteredList
  • Will output: 
    [0, 1, 2, 10, 11, 12, 20, 21, 22, 30] and so on
  • List Comprehensions with Functions
  • split function splits a string based on the characters that you give it.
  • For instance: 
    myString = 'My name is Howard. I am awesome'
myString.split('.')
  • This will output the following and split the above into two sentences: 
    ['My name is Howard', 'I am awesome']
  • If nothing is passed in, the split function will split on spaces. For example: 
    myString.split()
  • Will output: 
    ['My', 'name', 'is', 'Howard.', 'I', 'am', 'awesome']
  • To clean up the above output, we can use: ``` def cleanWord(word):

    Replaces anything with a . with an empty space

    The next function .lower() makes the string lowercase

    return word.replace(‘.’, ‘’).lower()

To use this in a List Comprehension, we use:

[cleanWord(word) for word in myString.split()]

* Calling one function , one after the other, is called `Chaining Functions`.
	* Be careful not to use it too often, as it can lead to long lines of code.
* Running the above function `[cleanWord(word) for word in myString.split()]` will result in an output of:

[‘my’, ‘name’, ‘is’, ‘Howard’, ‘I’, ‘am’, ‘awesome’]

* We can also clean and filter at the same time and have the lowercase words in the text.
	* Can do something like this:

[cleanWord(word) for word in myString.split() if len (cleanWord(word)) < 3]

* This will output all of the 1 and 2 letter words in the text, such as:

[‘my’, ‘is’, ‘i’, ‘in’]

* Nested List Comprehensions
* An example is:

This is splitting the original text into sentences, then performing an inner list comprehension on each sentence

[cleanWord(word) for word in sentence.split()] for sentence in myString.split(‘.’)]

* This will output a "list of lists", like a 2D structure.

[[‘my’, ‘name’, ‘is’, ‘Howard’], [‘I’, ‘am’, ‘awesome’]] ```

  • Allows you to write clean, readable and “Pythonic” code and is recommended by Python programmers.

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