Python as a language
Analogies between Python and human language
Words
Some words are English ("reserved words")
print
list
for
not
while
Some words are symbols
+
*
/
=
Punctuation
Group arithmetic operations with parentheses
(1 + 2) * 3
Create lists using square brackets and commas
[1, 2, 3]
Dependent clauses
"Expressions" in Python
1 + 2 + 3
(1 + 2 + 3) * 10
((1 + 2 + 3) * 10) / 7
Sentences
"Statements" in Python
print "A red circle"
red = 1
red_color = [1, 0, 0]
Paragraphs
"Blocks" in Python
Statements with the same amount of indentation
Essay
Essay (uh, oh ... the analogy is breaking down)
Beyond the language analogy
A "function" in Python
Predefined Python functions
range(5) => [0,1,2,3,4]
Defining a new Python "word"
def add_one(number):
return number + 1
current = 12
next = add_one(current)
Beyond the language analogy
A "script" in Python
A Python program
A set of functions and statements that implements some process
We will be writing Python scripts that will act just like Unix commands.
Beyond the language analogy?
"It should not be forgotten that communication is just one part
of language. Language is also a means of conceptualization, a way of
organizing the world, and thus is much more than mere communication."
Roland Barthes
Words now, pictures soon.
The language categories in Python
Naming
Choosing
Repeating
Grouping
Naming
"Variables" in Python
height = 71.9
digits = [0,1,2,3,4,5,6,7,8,9]
red = .3
green = .4
blue = .5
color = [red, green, blue]
image_filename = 'waterfall.0042.tif'
Choosing
"Conditionals" in Python
If (something is true) then (do this).
if red < .5:
print 'Dark red'
Choosing
"Conditionals" in Python
If (something is true) then (do this) else (do that).
if red < .5:
print 'Dark red'
else:
print 'Bright red'
Repeating
"Loops" in Python
Use each item in a list in turn
for n in [1, 2, 3]:
print n
Repeat while a condition holds
n = 1
while n < 10:
print n
n = n + 1
Grouping
"Blocks" defined by indentation
n = 1
while n < 10:
print n
n = n + 1
print n
Grouping
"Functions" are an abstract definition of a process
Uh...
Grouping
Functions process stuff
Grouping
Functions process input to produce output
Grouping
Functions take arguments and return a result
Grouping
Functions take arguments and return a result
def add(a, b):
return a + b
sum = add(98,2)
The basic programming language categories
Naming
"variables"
Choosing
"conditionals"
Repeating
"loops"
Grouping
"functions"
Naming
"variables"
Choosing
"conditionals"
Repeating
"loops"
Grouping
"functions"