The Basics: Synatx, Indentation, Comments, etc ...

Variables

Python has similar syntax to C/C++/Java so it uses the same convention for naming variables: variable names can contain upper and lower case character & numbers, including the underscore ( _ ) character.
Variable names are case sensitive
Variable names can't start with numbers or special characters (except for the undescore character)
Variables cannot have the same names as Python keywords

Keywords
and	assert	as	break	class	continue	def	del
elif	else	except	exec	finally	for	from	global
if	import	in	is	lambda	not	or	pass
print	raise	return	try	while	with	yield



In [3]:

    
# this is a correct variable name
variable_name = 10



In [4]:

    
# this is not a correct variable name - variable names can't start with a number
4tops = 5









    



  File "<ipython-input-4-fb63971d7854>", line 2
    4tops = 5
        ^
SyntaxError: invalid syntax



In [4]:

    
# here's the error generated from using a Python keyword - notice the color of the variable name: it's not the same 
# as the one in the cells below
finally = 7









    



  File "<ipython-input-4-c4cc63a2ab19>", line 3
    finally = 7
          ^
SyntaxError: invalid syntax



In [6]:

    
# these variables are not the same
distance = 10
Distance = 20
disTance = 30

print "distance = ", distance
print "Distance = ", Distance
print "disTance = ", disTance









    



distance =  10
Distance =  20
disTance =  30

Indentation and Code Blocks



In [7]:

    
x = 11

if x == 10:
    print 'x = 10'
else:
    print 'x != 10'
    print 'Done'

print "Bye now"









    



x != 10
Done
Bye now

Statements/Multiline statements

A new line signals the end of a statement



In [ ]:

    
# these are two separate statements
a = 4
b = 6

For multi-line statements, use the \ character at the end of the line



In [10]:

    
# use line continuation symbol (use with care)
a = 10 \
    + \
    10 + 10
print a

or put the multilines in ()



In [5]:

    
# use prenthesis (preferable way) to have a multiline statements
a = (10
    +            20 +    
    10 + 10)
print a

Comments

Comments begin after the # character which can appear anywhere on the line. Multiline comments begin and end with 3 matching ' or " characters.



In [6]:

    
# this is a line comment
a = 10 # this is also a line comment
'''
this line is indsie a multi-line comment
so is this
and this
'''
a = 100 # this is outside the multi-line comment

"""
This is another way to declare a multi-line comment
Inside it
inside it too
"""

a = 100 # this is outside the multi-line comment

You can put a comment inside a muliline statement



In [1]:

    
# multiline statement with comments
a = (10 # this is line 1
    +            20 +    # this is line 2
    10 + 10)
print a