Overview

Hour 1
- Data Types
- Decision Structures
Hour 2
- git demo
- py.test demo
Hour 3
- Graded lab exercise

Data Types

Recall that variables are like containers with labels
These containers also have "type." The type of a container determines the shape of stuff that can go inside.
Many data types in Python. Only need to know about: string, integer, float, and Boolean

Integer

Positive or negative whole numbers

Float

Short for floating point number
Positive or negative number with values to the right of the decimal place

Booleans

Named after the mathematician George Boole.
Booleans can be True or False. (The capitalization is important.)



In [ ]:

    
arthur = "king"
lancelot = -23
robin = 1.99
bedevere = True

How does Python know the data type?

Strings are delimited by quotation marks
Floats have decimals
Ints don't have decimals



In [28]:

    
arthur = "king"
type(arthur)









    Out[28]:





str



In [29]:

    
lancelot = -23
type(lancelot)









    Out[29]:





int



In [30]:

    
robin = 1.99
type(robin)









    Out[30]:





float



In [31]:

    
bedevere = True
type(bedevere)









    Out[31]:





bool

Reassigning Variables

Variables can change values after initial assignment



In [32]:

    
galahad = 1
galahad = 57
galahad









    Out[32]:





57

Variables can also change types after initial assignment



In [34]:

    
patsy = 2
patsy = "Clip clop"
type(patsy)









    Out[34]:





str

Value can also be forced to take on a data type
- int() converts a value to an integer
- float() converts a value to a float
- str() converts a value to a string
But it doesn't always make sense to so



In [40]:

    
zoot = float(5)
zoot = 5.0
zoot
type(zoot)
zoot = "5"
type(zoot)
zoot = str(5)
zoot
type(zoot)









    Out[40]:





str



In [49]:

    
arthur = "king"
galahad = "5"

print(arthur + galahad)

robin = 4
bedevere = 5.0

print(robin * bedevere)
int(20.7)









    



king5
20.0






    Out[49]:





20

Ranges of Data Types

It is possible to have numbers that are too big or too small to be represented by Python.
Integers range from -2**63 to 2**63 - 1
Floats range from 2.2250738585072014e-308 to 1.7976931348623157e+308



In [ ]:

    
import sys
print(sys.maxint)
print(sys.float_info)

Decision Structures

So far, we've been writing programs that do the same thing repeatedly. If order for a program to be more reactive, we need a way for it to make decisions. Depending on whether something is the case, it takes one action or another.

Here's the general form of an if statement

if *condition*: statement statement etc.



In [51]:

    
cold = True

if cold:
    print("Wear a coat.")

Boolean Expressions and Relational Operators



In [56]:

    
x = 1
y = 2
y != x









    Out[56]:





True

Comparing Strings

Characters are stored as ASCII codes
- Uppercase A-Z are numbers 65-90
- Lowercase a-z are 97-122
- Digits 0-9 are 48-57
String comparisons use these codes



In [62]:

    
name1 = "Mary1"
name2 = "Mary"

name1 < name2









    Out[62]:





False

Putting Together Concepts

Let's put the if statement together with Boolean expressions



In [64]:

    
temperature = 10

if (temperature < 12):
    print("Wear a coat.")









    



Wear a coat.

Alternate Paths



In [69]:

    
temperature = 39.5

if temperature < 40.0:
    print("A little cold, isn't it?")
    print("Wear a coat")
else:
    print("Nice weather we're having")
    print("Don't wear a coat")

print("Done the if-statement")









    



A little cold, isn't it?
Wear a coat
Done the if-statement

Nested Decision Structure



In [72]:

    
salary = 40000
years_on_the_job = 2

if salary >= 30000:
    if years_on_the_job >= 2:
        print("You qualify for the loan")
    else:
        print("You must have been on your current job for at least two years to qualify.")
else:
    print("You must earn at least $30,000 per year to qualify.")









    



You qualify for the loan

Multiple Nested Decision Structures



In [83]:

    
score = 45

if score >= 90:
    print("Your grade is A")
elif score >= 80:
    print("Your grade is B")
elif score >= 70:
    print("Your grade is C")
else:
    print ("Restart. Try again.")

print("Done with if-statement")









    



Restart. Try again.
Done with if-statement

Rule 5

Test your code, often and thoroughly.

py.test

A test framework for Python. (There are many.)

We use this to grade. For subsequent assignments, you'll be writing test cases too.

Lab Exercise

Each student should fork the repo at:

https://github.com/benevolentprof/inf1340-2015-labs

Then clone into PyCharm

Do the exercise, commit and push as you go along.



In [ ]: