Python Programming Essentials - M6 - Code Blocks and Indentation

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Statements, Code Blocks and Indentation
Pavan Verma
Python Programming Essentials
1
@YinYangPavan

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Python statements
 A statement is a one Python instruction
 Most of the time, there is exactly one Python
statement per line
>>> x = 4 + 6
>>> y = x**2
>>> print y
100
2

Multiple statements on one line
 It’s possible to have multiple statements,
separated by semi-colon, on a single line
 Doing so is NOT recommended as it reduces
code readability
>>> x = 4 + 6; y = x**2; print y
100
3

Statements can span multiple lines
 There are two ways to make a statement span
multiple lines
 Use it if it improves code readability by
breaking a very long statement
4
>>> x = 4 +
6
>>> x
10
>>> x = (4
+
6)
>>> x
10

Code blocks
 A code block is a set of statements that will be
executed together, one after the other
 if statements, for loops, while loops, functions, are all
code blocks
if x > 10:
is_greater = True
print "Greater than 10"
else:
is_greater = False
print "Not greater than 10"
5

Code blocks and Indentation
 Code blocks have no explicit begin or end. There
are no explicit braces, brackets, or keywords.
 Code blocks are defined by their indentation
• Indenting starts a block and unindenting ends it
• The only delimiter is a colon (:) and the indentation
of the code itself
 This means that whitespace is significant, and
must be consistent
6

Sample code blocks
def fib(n):
print 'n = ', n
if n > 1:
return n * fib(n-1)
else:
print 'end'
return 1
7

Sample code blocks (2)
8
def fib(n):
print 'n = ', n
if n > 1:
return n * fib(n-1)
else:
print 'end'
return 1

9
def fib(n):
print 'n = ', n
if n > 1:
return n * fib(n-1)
else:
print 'end'
return 1

10
def fib(n):
print 'n = ', n
if n > 1:
return n * fib(n-1)
else:
print 'end'
return 1

Indentation Tips
 Use 4 spaces per indentation level
 Spaces are the preferred indentation method
 Use spaces for indentation; not tabs
• 1 tab == 1 indent level
 Python 3 explicitly disallows mixing the use of
tabs and spaces for indentation
11

Summary
 Statements
 Relationship between Python statements
and lines
 Code blocks
 Relationship between code blocks and
indentation in Python
12

Python Programming Essentials - M6 - Code Blocks and Indentation

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