Download Running Python Program - Yang Zhang

Xi Wang
Yang Zhang
1. Easy to learn
2. Clean and readable codes
3. A lot of useful packages, especially for web
scraping and text mining
4. Growing popularity
 Installing Python
 https://www.python.org/
 Online Learning resources
 How to Think Like a Computer Scientist
 http://www.openbookproject.net/thinkcs/python/engli
sh2e/
 Code Academy
 https://www.codecademy.com/tracks/python
 Edx: Introduction to Computer Science and
Programming Using Python
 https://www.edx.org/
1. Python Shell
 Windows: command prompt
 Mac: terminal
2. Script
3. Integrated Development Environment (IDE)
1. Write a program in a text editor and save it as a
.py file.
2. Run the script in a Python shell.
 An IDE normally consists of a source code editor,
build automation, and a debugger.
 Python IDEs
 https://en.wikipedia.org/wiki/Comparison_of_integr
ated_development_environments
 Example: Enthought Canopy
1. Variables
2. Functions
3. Conditionals
4. Iteration
 Slides and example codes can be downloaded from
http://yang-zhang.weebly.com/teaching.html
 Everything in a Python program belongs to a data
type:
>>> type(5)
<type ‘int’>
>>> type(1.23)
<type ‘float’>
>>> type(“Hello, World!”)
<type ‘str’>
>>> type(‘Hello, Iowa!’)
<type ‘str’>
>>> type(‘5’)
<type ‘str’>
>>> type(True)
<type ‘bool’>
>>> type(False)
<type ‘bool’>
 Data types can be changed:
>>> float(5)
5.0
>>> str(5)
‘5’
>>> int(1.9)
1
>>> int(‘5’)
5
>>> int(True)
1
 A variable is a name that refers to a value.
 The assignment statement creates new variables
and gives them values:
>>> message = “What’s up?”
>>> n = 18
>>> pi = 3.14
 Print statement shows the content of a variable:
>>> print message
What’s up?
>>> print n
18
>>> print pi
3.14
 Variables can be changed:
>>> count = 10
>>> count = count – 1
>>> print count
9
>>> count -= 1
>>> print count
8
 Python is a calculator:
>>> x = 10
>>> y = 2
>>> z1 = 3
>>> z2 = 3.0
>>> x / y
5
>>> x / z1
3
>>> x /z2
3.3333333333333335
 A function is a named sequence of statements that
performs a desired operation.
 Python has many useful built-in functions. For
example:
>>> type(5)
Int
>>> abs(-10)
10
>>> max(1,2,3)
3
 In Python, the syntax for a function definition is:
def NAME(PARAMETERS):
STATEMENTS
Be cautious with indentation!
 For example:
>>> def myMean(a,b):
return (a+b)/2
>>> myMean(3,5)
4
 Default parameter values
>>> def discArea(r, pi=3):
return pi*(r**2)
>>> discArea(2)
12
>>> discArea(2, 3.14)
12.56
>>> discArea(r=2, pi=3.14)
12.56
 A module is a neatly packaged set of functions.
Some come with Python, others need to be
installed.
 For example, to know your current working
directory:
>>> import os
>>> os.getcwd()
'C:\\Users\\Yang'
>>> from os import getcwd
>>> getcwd()
'C:\\Users\\Yang'
 There are only two Boolean values.
 True
 False
 A Boolean expression returns a Boolean value.
>>> 5 == 5
True
>>> 5 == 6
False
x=5
y=6
>>> x == y
False
>>> x != y
True
>>> x > y
False
>>> x < y
True
What will happen if we type x = y?
 Logical operators connect multiple Boolean
expressions.
>>> 3 > 0 and 3 < 5
True
>>> 3 < 2 or 3 < 1
False
>>> not(5 > 6)
True
 Conditional statements take a form like this:
if BOOLEAN EXPRESSION:
STATEMENTS
>>> x = 5
>>> if x > 0:
print 'x is positive.'
x is positive.
 Alternative Execution
>>> def isEven(x):
if x % 2 == 0:
return True
else:
return False
>>> isEven(5)
False
>>> isEven(6)
True
 Conditionals can be chained:
>>> x = 5
>>> y = 6
>>> if x < y:
print x, "is less than", y
elif x > y:
print x, "is greater than", y
else:
print x, "and", y, "are equal"
5 is less than 6
 Conditionals can be nested:
>>> if x == y:
print x, "and", y, "are equal"
else:
if x < y:
print x, "is less than", y
else:
print x, "is greater than", y
5 is less than 6
 Iteration is repeated execution of a set of
statements.
1. The while statement
2. The for statement
 The while statement
>>> def countdown(n):
while n > 0:
print n
n = n-1
print "Blastoff!"
>>> countdown(3)
3
2
1
Blastoff!
 The for statement
>>>
for x in 'Iowa':
print x
I
o
w
a
 Introduction to Python
 Introduction to R
 Stata Programming
 Introduction to ArcGIS
 Multilevel Modeling in R and Stata
http://ppc.uiowa.edu/node/3608