programming with python

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{ Introduction To Programming with Presenters: Patrick Smyth & Kenneth Ezirim {

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Page 1: Programming with python

{

Introduction To Programming

with

Presenters: Patrick Smyth & Kenneth Ezirim{

Page 2: Programming with python

What is Python?

Page 3: Programming with python

What is Python?• Programming Language

- Tells computer what to do

• Interpreted Language

- Different from Compiled Languages

- Executes Program Line by Line

- Turns code into 0s and 1s for

Page 4: Programming with python

Requirements for Python• To program and run your Python code

- Need a Python Interpreter

- Download and Install IDLE

- Check if Python is installed using command

“python -V”

- Should show the version of Python installedIDLE and Python already computers Let’s dive in!!!

Page 5: Programming with python

Simple ProgramsOpen IDLE and type the following

Basic Math in Python

>>> print “Hello, World!”

>>> 1 + 12

>>> 20 * 15300

>>> 30 / 56

Command Name

+ Addition

- Subtraction

* Multiplication

/ Division

% Remainder

** Exponent

>>> 4 – (2 + 4)-2

>>> 2 * “Hello, World!”

>>> #I am a comment, Fear my wrath!!!

Comments, Please

Page 6: Programming with python

Writing Python code in a file

-       Very easy to create

-       simple text document

-       you can open them in notepad

-       save with a filename and an extension “.py”

Page 7: Programming with python

Writing Python code in a fileOpen notepad and type the following:

#Program: maryjane.py#Simple program

print “Mary Jane had a small cat”print "it's fleece was white as snow;"print "and everywhere that Mary went",print "her lamb was sure to go.”

Save file as maryjane.py

Page 8: Programming with python

Writing Python code in a file

Using the IDLE environment

-       File > Open > Search for  maryjane.py

-       Run > Run Module to run program

Note:

-       Comment was not printed

-       3rd and 4th lines were merged

-     maryjane.py can also be run from the

command line

>>> python maryjane.py

Page 9: Programming with python

Storing Values in Python: Variables

-  Stores values

- Values can be changed

- Let’s write a program that  uses variables#Program: variables.py#examples using variablesv = 1print “The value of v now is”, vv = v + 1print “The value of v is itself plus one, which is equal to ”, vu = v * 2print “The value of u equals value in v multiplied by 2,”,print “ which is equal to ”, u

Page 10: Programming with python

Storing Values in Python: Variables

Variables can also store text, for instance

text1   = “Good Morning”text2 = “Mary Jane”text3 = “Mrs.”print text1, text2sentence = text1 + “ ” + text3 + text2print sentence

Expected Output:Good Morning Mary JaneGood Morning Mrs. Mary Jane

Next we look at conditionals and loops…

Page 11: Programming with python

Conditionals & Loops

• You need a program to do something a number of times

• For instance, print a value 20 times?

'a' now equals 0 As long as 'a' is less than 10, do the following:

Make 'a' one larger than what it already is. print on-screen what 'a' is now worth.

a = 0while a < 10 :

a = a + 1

print a

The ‘while’ Loop:

Page 12: Programming with python

Conditionals & Loops

while {condition that the loop continues}:

{what to do in the loop}

{have it indented, usually four spaces or tab}

{the code here is not looped because it isn't indented}

#EXAMPLE #Type this in, see what it does x = 10 while x != 0:

print x x = x - 1

print "wow, we've counted x down, and now it equals", x print "And now the loop has ended."

Page 13: Programming with python

Conditionals & LoopsBoolean Expressions (Boolean... what?!?)- what you type in the area marked {conditions that the loop continues}

Expression Function< less than<= less that or equal to> greater than>= greater than or equal

to!= not equal to<> not equal to

(alternate)== equal to

Examples

• My age < the age of the person sitting opposite to me• Cash in my wallet == 100• Cost of an iPhone is >= 660

Page 14: Programming with python

Conditionals & Loops• Conditional – a section of code that is executed if

certain conditions are met

• Different from While loop – run only once!

• Most common is the IF - statement

Syntax:

if {conditions to be met}: {do this}{and this} {and this}

{but this happens regardless}{because it isn't indented}

Example:

y = 1if y == 1:

print ‘y still equal to 1’

x = 10if x > 11:

print x

Page 15: Programming with python

Conditionals & Loops

Conditionals can be used together with a loop. For instance,

print "We will show the even numbers up to 20" n=1while n <= 20:

if n % 2 == 0: print n

n=n+1print "there, done."

Note:

n % 2 implies the remainder after the value in n is

divided wholly by 2. The expression is read as ‘n

modulus 2’. For instance, 4 % 2 = 0 and 7 % 2 = 1.

Page 16: Programming with python

Conditionals & Loops

- When it Ain't True

Using 'else' and 'elif’ when IF conditions fails

- ‘else’ simply tells the computer what to do if

the conditions of ‘if’ are not met

- ‘elif’ same as ‘else if’

- ‘elif’ will do what is under it if the conditions

are met

Page 17: Programming with python

Conditionals & Loops

a = 1if a > 5:

print "This shouldn't happen." else:

print "This should happen."

z = 4if z > 70:

print "Something is very wrong" elif z < 7:

print "This is normal"

Page 18: Programming with python

Conditionals & LoopsGeneral Syntax:

if {conditions}: {run this code}

elif {conditions}: {run this code}

elif {conditions}: {run this code}

else: {run this code}

- You can have as many elif statements as you

need

- Anywhere from zero to the sky.

- You can have at most one else statement

- And only after all other ifs and elifs.

Page 19: Programming with python

Conditionals & LoopsGeneral Example:

a = 10 while a > 0:

print a if a > 5:

print "Big number!" elif a % 2 != 0:

print "This is an odd number" print "It isn't greater than five, either"

else: print "this number isn't greater than 5" print "nor is it odd" print "feeling special?”

a = a - 1print "we just made 'a' one less than what it was!"print "and unless a is not greater than 0, we'll do the loop

again print "well, it seems as if 'a' is now no bigger than 0!"

Page 20: Programming with python

Python and Functions Writing interactive program involves:

- User input

- Function to process user input

- Function Output

What is a Function?

-       self-contained code

-       perform a specific task

-       can be incorporated in larger programs

-       can be used more than once

Page 21: Programming with python

Python and FunctionsUsing functions

- Python have predefined functions

- give an input and get an output

- calling a function

Function_Name(list of parameters)

For instance,

a = multiply(70)

Computer sees

            a = 350Note: multiply() is not a real function!!!

Page 22: Programming with python

Python and FunctionsSo what about a real function?

Let’s try a function called raw_input()

#Program: echo.py

#this line makes ‘in' equal to whatever you type in

in = raw_input("Type in something, and it will echoed on

screen:")

# this line prints what ‘in' is now worth

print in

The function raw_input asks the user to type in something. It then turns it into a string of text.

Page 23: Programming with python

Python and FunctionsAssuming you typed “hello”, the computer will

see the program as:

in = “hello” print “hello”

Note:

- Variable ‘in’ is stored value

- Computer does not see ‘in’ as in

- Functions are similar: input and output

Page 24: Programming with python

User-defined Functions- Decide what your function does

- Save time looking other people’s functions

- Use in subsequent programs

Syntax:def function_name(parameter_1,parameter_2):

{this is the code in the function}

{more code}

{more code}

return {value to return to the main program}

{this code isn't in the function}

{because it isn't indented}

Page 25: Programming with python

User-defined Functions

# Below is the function def hello():

print “HELLO" return 1234

# And here is the function being used print hello()

So what happened?

1. When 'def hello()' was run, a function called 'hello' was

created

2. When the line 'print hello()' was run, the function 'hello'

was executed

3. The function 'hello' printed ‘HELLO’ onscreen, then

returned the number '1234' back to the main program

4. The main program now sees the line as 'print 1234' and

as a result, printed '1234’

Page 26: Programming with python

User-defined Functions#Program: add.py#function to adddef add(a, b):

sum = a+ breturn sum

#program starts herea = input(“Add this: ”)b = input(“ to this: ”)print a , “+”, b, “=”, add(a,b)#program ends here

print a , “+”, b, “=”, add(input(“Add this: ”), input(“ to this: ”))

{

Function input returns what you typed in, to the main

program.

But this time, it returns a type that is a number, not a string!

Page 27: Programming with python

Tuples, Lists and DictionariesTuple

months = ('January','February','March','April','May','June',\'July','August','September','October','November',' December')

List

cats = ['Tom', 'Snappy', 'Kitty', 'Jessie', 'Chester']

Dictionary

phonebook = {'Andrew Parson':8806336, \'Emily Everett':6784346, 'Peter Power':7658344, \'Lewis Lame':1122345}

Page 28: Programming with python

Tuplesmonths = ('January','February','March','April','May','June',\'July','August','September','October','November',' December')

- Used for coordinate pairs, employee records in database

- Python organizes the values by indexing >>> months[0] ‘January’

- Create tuple from command line>>> t = 12345, 54321, ‘hello!’>>> t>>> (12345, 54321, ‘hello’)

- Determine size of tuple>>> len(t)3

- Packing and Unpacking tuple >>> x , y, z = t >>> z ‘hello’

Page 29: Programming with python

Listscats = ['Tom', 'Snappy', 'Kitty', 'Jessie', 'Chester']

Print size of list: print len(cats)

Print an element of a list: print cats[2]

Print a range of a list: print cats[0:2]

Add a value to the list:

cats.append(‘Catherine’)

Delete an element of a list: del cats[1]

Page 30: Programming with python

Dictionariesphonebook = {'Andrew Parson':8806336, 'Emily Everett':6784346, \ 'Peter Power':7658344, 'Lewis Lame':1122345}

Access a person’s phone number:>>> phonebook[‘Andrew Parson’]8806336

Change a person’s phone number:>>> phonebook[‘Lewis Lame’] = 5432211

Add a person to the phonebook>>> phonebook['Gingerbread Man'] = 1234567

Delete a person from phonebook>>> del phonebook['Andrew Parson']

Page 31: Programming with python

Dictionaries: Sample program#define the dictionaryages = {}#add names and ages to the dictionaryages['Sue'] = 23ages['Peter'] = 19ages['Andrew'] = 78ages['Karren'] = 45

#function keys() - is function returns a list of the names of the keys.print "The following people are in the dictionary:”, ages.keys()

#Use the values() function to get a list of values in dictionary.print "People are aged the following:", ages.values()

#You can sort lists, with the sort() functionkeys = ages.keys();keys.sort()print keys

values = ages.values()values.sort()print values

Page 32: Programming with python

The For loopUsed to iterate through values in a list

# Example 'for' loop

# First, create a list to loop through:

newList = [45, 'eat me', 90210, "The day has come, \

the walrus said, to speak of many things", -67]

# create the loop:

# Go through newList, and sequentially puts each list item

# into the variable value, and runs the loop

for value in newList:

print value

Page 33: Programming with python

The For loop#cheerleading program

word = raw_input("Who do you go for? ")

for letter in word:

call = "Gimme a " + letter + "!"

print call

print letter + "!"

print "What does that spell?"

print word + "!"

Page 34: Programming with python

Operations with ListsConditionals:>>> sent = ['No', 'good', 'fish', 'goes', 'anywhere', 'without', 'a', 'porpoise', '.'] >>> all(len(w) > 4 for w in sent) False >>> any(len(w) > 4 for w in sent) True

Slicing:

>>> raw = ‘Man in the mirror’>>> raw[:3]Man>>> raw[-3:]ror>>> raw[3:]‘ in the mirror’

Page 35: Programming with python

Importing Modules- Import modules using the keyword ‘import’

- can be done via command line as well as in text file mode

Example:

>>> import random

>>> random.randint(0,10)

3

Page 36: Programming with python

CreditsSome materials from Sthurlow.com