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Understanding whitespace in Python

From: Python 3 Essential Training

Video: Understanding whitespace in Python

Whitespace is significant in Python in ways that you may not be accustomed to, if you are familiar with other scripting languages. Let's go ahead and make a working copy of syntax.py, and we can look at whitespace in Python. Call it syntax-whitespace.py. Go ahead and open that up, and you will notice that this main function consists of one statement, a print statement, and that print statement is indented four spaces, ands that actually tells Python that this print statement is associated with this main function.

Understanding whitespace in Python

Whitespace is significant in Python in ways that you may not be accustomed to, if you are familiar with other scripting languages. Let's go ahead and make a working copy of syntax.py, and we can look at whitespace in Python. Call it syntax-whitespace.py. Go ahead and open that up, and you will notice that this main function consists of one statement, a print statement, and that print statement is indented four spaces, ands that actually tells Python that this print statement is associated with this main function.

It's actually the body of the main function. Four spaces are traditional in Python. You can use two. You can use one. It will work just as well. It does have to be consistent. In other words, if I have more than one line here, and if that other line is indented, say three spaces instead of four, if I save that and run it, you will see that I get a syntax error, and it says unindent does not match any outer indentation level.

So Python got confused. We indented this one four spaces, we indented this one three spaces and it just got confused. It didn't know what to do with that. So the indention has to be the same amount. Save that and run it, and we will see that that works. Now if I take this second line and I indent it back at the same level as the function definition, then it is no longer part of the body of that function. So what will happen when I run this is it will actually see this line, this is another line, before the syntax file and the reason for that is because that will get executed on the first pass through here before we call main.

main gets called at the end of the file. So this line will be printed first and then this line. So we will save that, and we will run it, and you see this is another line, and then this is the syntax file. So, by bringing the indentation out to the same level as the definition, it is now no longer part of the body of that function. We will go ahead and indent that again and save it and run it, and we see that it works as we expect with this second line after the first line.

So indentation as whitespace is significant in Python because Python doesn't use curly braces, or any other characters, to indicate the body of a function, or what they a call suite - what we might call a block of code that's - associated with a particular control structure. These indents are used for conditionals. They are used for classes. They are used for any place where you might need to associate a block of text with a particular control structure. Now there is one circumstance where the indentation and the whitespace is not actually significant.

If you have just one line of code in a particular structure - and that's all there is, there is not more than one line of code - that one line of code can be on the same line as the control structure itself. So if I put this print here - and I can put a space, or not put a space, or put several spaces - it will work exactly the same. I save this and run it, you see that it still works. Just like this 'if' statement down here has one line of code, which is the function call for main, now this function definition for main has just one line of code, the print, and in this case the whitespace is not significant.

I can have five spaces, I can have one space, and it still runs just the same. That's a special case for whether its just one line of code in a particular structure. Under most circumstances, where you have a function, or a class, or something like that, and you have more than one line of code, you will see the indentation used, and four spaces is traditional, and the indentation has to be consistent all the way through the block or the suite of code.

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This video is part of

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Python 3 Essential Training

87 video lessons · 39513 viewers

Bill Weinman
Author

 
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  1. 5m 14s
    1. Welcome
      1m 32s
    2. Understanding prerequisites for Python
      2m 4s
    3. Using the exercise files
      1m 38s
  2. 33m 29s
    1. Getting started with "Hello World"
      4m 43s
    2. Selecting code with conditionals
      4m 45s
    3. Repeating code with a loop
      4m 13s
    4. Reusing code with a function
      2m 43s
    5. Creating sequences with generator functions
      2m 46s
    6. Reusing code and data with a class
      4m 39s
    7. Greater reusability with inheritance and polymorphism
      7m 17s
    8. Handling errors with exceptions
      2m 23s
  3. 22m 32s
    1. Installing Python 3 and Eclipse for Windows
      11m 24s
    2. Installing Python 3 and Eclipse for Mac
      11m 8s
  4. 28m 0s
    1. Creating a main script
      3m 27s
    2. Understanding whitespace in Python
      4m 8s
    3. Commenting code
      3m 28s
    4. Assigning values
      3m 37s
    5. Selecting code and values with conditionals
      4m 46s
    6. Creating and using functions
      3m 54s
    7. Creating and using objects
      4m 40s
  5. 31m 23s
    1. Understanding variables and objects in Python
      2m 46s
    2. Distinguishing mutable and immutable objects
      2m 41s
    3. Using numbers
      3m 34s
    4. Using strings
      6m 38s
    5. Aggregating values with lists and tuples
      4m 55s
    6. Creating associative lists with dictionaries
      4m 24s
    7. Finding the type and identity of a variable
      4m 45s
    8. Specifying logical values with True and False
      1m 40s
  6. 9m 42s
    1. Selecting code with if and else conditional statements
      2m 22s
    2. Setting multiple choices with elif
      2m 14s
    3. Understanding other strategies for multiple choices
      2m 38s
    4. Using the conditional expression
      2m 28s
  7. 11m 26s
    1. Creating loops with while
      1m 27s
    2. Iterating with for
      3m 54s
    3. Enumerating iterators
      3m 22s
    4. Controlling loop flow with break, continue, and else
      2m 43s
  8. 23m 28s
    1. Performing simple arithmetic
      2m 14s
    2. Operating on bitwise values
      3m 30s
    3. Comparing values
      3m 32s
    4. Operating on Boolean values
      2m 59s
    5. Operating on parts of a container with the slice operator
      6m 52s
    6. Understanding operator precedence
      4m 21s
  9. 11m 34s
    1. Using the re module
      1m 4s
    2. Searching with regular expressions
      3m 12s
    3. Replacing with regular expressions
      3m 29s
    4. Reusing regular expressions with re.compile
      3m 49s
  10. 9m 10s
    1. Learning how exceptions work
      1m 18s
    2. Handling exceptions
      4m 15s
    3. Raising exceptions
      3m 37s
  11. 23m 1s
    1. Defining functions
      6m 23s
    2. Using lists of arguments
      2m 26s
    3. Using named function arguments
      4m 32s
    4. Returning values from functions
      1m 55s
    5. Creating a sequence with a generator function
      7m 45s
  12. 47m 29s
    1. Understanding classes and objects
      5m 12s
    2. Using methods
      6m 12s
    3. Using object data
      10m 4s
    4. Understanding inheritance
      5m 11s
    5. Applying polymorphism to classes
      7m 13s
    6. Using generators
      9m 48s
    7. Using decorators
      3m 49s
  13. 18m 54s
    1. Understanding strings as objects
      3m 25s
    2. Working with common string methods
      5m 24s
    3. Formatting strings with str.format
      5m 31s
    4. Splitting and joining strings
      2m 49s
    5. Finding and using standard string methods
      1m 45s
  14. 25m 27s
    1. Creating sequences with tuples and lists
      4m 6s
    2. Operating on sequences with built-in methods
      5m 50s
    3. Organizing data with dictionaries
      4m 56s
    4. Operating on character data with bytes and byte arrays
      10m 35s
  15. 11m 46s
    1. Opening files
      2m 4s
    2. Reading and writing text files
      4m 33s
    3. Reading and writing binary files
      5m 9s
  16. 21m 27s
    1. Creating a database with SQLite 3
      6m 56s
    2. Creating, retrieving, updating, and deleting records
      7m 31s
    3. Creating a database object
      7m 0s
  17. 18m 27s
    1. Using standard library modules
      8m 0s
    2. Finding third-party modules
      5m 47s
    3. Creating a module
      4m 40s
  18. 23m 11s
    1. Dealing with syntax errors
      8m 19s
    2. Dealing with runtime errors
      4m 0s
    3. Dealing with logical errors
      4m 22s
    4. Using unit tests
      6m 30s
  19. 19m 56s
    1. Normalizing a database interface
      6m 39s
    2. Deconstructing a database application
      8m 9s
    3. Displaying random entries from a database
      5m 8s
  20. 29s
    1. Goodbye
      29s

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