A Beginner’s Guide to Python Programming

8/12/2019 A Beginners Guide to Python Programming

1/15

A Beginners Guide to Pyth

Python Version: 3.3.4


2/15

Contents

For Starters (IDLE)

Hello World!

Variables Operators

The IF statement

ElseIF and Else

Functions

Arguments For Loop

While Loop

Strings

Lists

Tuples


3/15

For Starters Python IDLE (shown right)

On installation, IDLE (Python GUI) should be found in your startmenu files

On Windows 7: Start > All Programs> Python 2.7> IDLE

On Windows 8: Start > All Apps > Python 2.7> IDLE

Python can be programmed in any text editor andsaved as a .py file, but for the sake of this tutorial,we will be using the interpreter to cover the pythonsyntax(the way it is written) and other basicprogramming concepts.

Note that the interpreter functions like a commandprompt in Windows. You cannot delete items once

the ENTER key is pressed. Mistakes should be of noconcern, howeverif an error occurs simply tryagain on the next line until you get the desiredoutput, or restart IDLE if youd like to work from aclean slate.

The Python interpreter, called IDLE, ready


4/15

Hello World

Next to the three greater than signs (>>>), type: print

(Hello World), then press the ENTER key. Note that

the function print was displayed in purple, the string

(Hello World) was displayed in green, and that the

printed output is displayed in blue. Color-coded

indicators are a good way of knowing that something

was typed correctly as you go. Try typing a different

string inside the apostrophes and seeing the result,

like print(Python!). This is telling IDLE to show

whatever string

Note what happens when I forgo

second apostrophe() to the strin

The interpreter takes the second

end of the statement, and withou

message will be returned. A Syn

when something was typed inco

(as opposed to compiling incorre

beyond the scope of this tutorial

section was highlighted in red an

written in red. Should you make

try again on the next line.


5/15

Simple Math A simple math problem is a good way to

introduce the concept of variables:

A variable in programming, much like math, is

a way to store a value in memory for later use.

Variables are the backbone of programming.

Here is a few ways they are used:

To store user input in a place that can be used

later (in a function, perhaps)

To store the result of functions and loops, for

use in other functions and loops.

To allow the values in program to changedynamically (while the program is running)

The math problem on the right stores the values

of a and b, and then uses these values to

designate the value ofz (the third line means z

equals a divided by b)


6/15

Operators Basic operators in Python are the same as they

are in mathematics: + (add)

- (subtract)

* (multiply)

/ (divide)

Python uses PEMDAS in the absence of

distinguishing parenthesis. For example: 7 + 8 * 4 is seen as 7 + (8 *4) not (7+8) * 4, because

multiplication is first in order of operations.

The examples on the right shows three slightly

more complicated operators:

The modulus operator (%), which takes the value of thenumber on the left, divides it by the number on the right,

and returns the remainder.

The exponent operator (**) means, to the power of, so

2 to the second power is written: 2**2

The floor division operator(//) is the same as division,

except it rounds the result down to the nearest whole

number.

Translati

1) X is e

of 10

96. T

2) Y is e

powe3) Z is e

21, ro

near

/ 21

roun

4) For g

stora

showwhic

the e

(64)

Th IF


7/15

The IF statement The if statement is a conditionalstatement. It is

where the previous concepts are applied to the

creation of logic within a program.

A statementis a command given to a program

to execute what comes afterward, so the

program knows when it reads the word if that

a condition is to follow.

The breakdown of an if statement is as follows:

If (certain conditions are true):

then (execute this code)

Note that there is a double equal (==) operator

qualifying the statement. The double equal is

used in place of a singular equal sign to

differentiate between a comparison (n==1) and a

declaration (n=1).

Translation:

1) The variable N is equal to 40.

2) The if statement asks if the varia

(which is true). Note the colon (

condition.

3) The print command will executewhich precedes it is true. Since n

the condition is satisfied and the

executes.

4) Try the same statement with valu

like setting (n=40) and then havin

(if n ==44: ). Notice that nothing

El IF d El


8/15

Else IF and Else The Else IF and Else statements are extensions of the IF

statement, which gives the program more decisions to make in

a function. This method is used when there are two or more

conditions that need to be satisfied.

The breakdown of an IF-ElseIF-ELSE statement is as follows:

If(certain conditions are true):

then (execute this code)

Else, if (this condition is true, but the previous conditions arent)

then (execute this code instead)

Else (assume that neither of the previous conditions are true)

And (execute this code instead)

IMPORTANT: When the elif and else statements cannot

be indented in the interpreter. If pressing return

automatically indents the new line, press backspace and it

should appear as it does on the right.

Note in the example on the right that thegreater than or

equal to sign (>=) is introduced as an operator. It, along

with less-than-or-equal-to (


9/15

Functions Functions are a means of separating code

utilizing statements that apply to different

processes over and over without retyping

them.

Functions use the keyword def to indicate

that a function is to follow. The name of a

functions does not contain spaces, and

should be unique within your program:

def functionName():

Above, functionName is where you place

the name of the function you are creating.

The parenthesis () next to the function

name is for passing arguments, which will

be covered in the next chapter

NOTE: For this slide and the next, you want

to leave the IDLE interpreter and use the

IDLE editor. From the file menu, select File,

then select New File. Note that the window

is now blank, and it should look like a blank

text editor.

Translation:

1) The rear window is

absence of text at t

function with the k

myfunction(), and d

happen when the f

to print Testing my

2) In the next part, I c

created in order to

typing it by name w

to it, like so: myfun

3) To test the function

select Run from the

Run Module, or sim

to save the file; it d

what its called as l.pyw) isnt changed

4) An IDLE interpreter

will open, showing

function, told the in

print something wh

then I called the fu

A t


10/15

Arguments Arguments are a way to pass

values between functions. This is

the purpose of the parenthesis ()

next to a function declaration. It

is left blank if there are no

arguments to be passed.

Using arguments in functions are

useful when you want to calculate

a set of variables with one

function, then calculate the same

variables a different way inanother.

Remember to place a colon (:)

after the function definition to

avoid an error.

Translation:

1) Using the same f

previous slide, I e

and b as argume

2) The code on the

interpreter to pra+b.

3) The function was

values 45 and 55

compiler automa

variables a and b

provided. These

inserted into the

which becomes:4) After running the

the interpreter o

and displays the

F

L


11/15

For Loops

A loop in programming is a way of telling the

program to execute code. For example, if you had

a group of people at a party and you wanted to

make sure they all got plates, you would say forevery person at the party, hand out one plate.

This a simplification of the process, but it

expresses the same concept.

The example on the right also introduces the

range function. As it sounds, the function returns

the range between a given set of items. Therange function can be use in many ways other

than the range(start, stop) shown here. Notice

that the 6 is not counted.

Translation:

1) The loop reads: for every none to six, print n.

2) The loop will pass continue

print(n) until it reaches the

limit. Try inserting differen

the range to understand ho

counting works.

While Loop


12/15

While Loop WHILE loops are similar to FOR loops, in that both

provide a method for repeating code until conditions

are met. The difference between the types is that a FOR

loop will execute a designated amount of time, whereas

a WHILE loops executes until certain conditions are met(make a while loop similar to an if statement that

repeats).

This example introduces the incremental operator

called add AND, which is written as +=. It means

increase the value on the left by the increment on the

right. In a loop, the value will continue to climb at therate of the value on the right.

Translation:

1) The value ofx is set at 0.

2) The loop reads, as long as x is lesvalue of x

3) The add AND operator (+=) tells

increment, so x starts at 0, then

forth, each time the loop occurs

4) The output stops when it reache

print function because it is after

If you would want the loop to sto

the limit to 6.

Strings


13/15

Strings A string, or string literal, is a type of variable that

indicates the value is to be treated like a literal word. It

is notated by quotation marks , and should show up in

the editor/interpreter in green.

Strings are useful for storing text in a program, whichcan be used later in a number of ways, including:

Taking entered text, like a name, and assigning it to a

variable.

Checking to see if entered text matches a string value

already in a program, like a user password.

Displaying text when a certain action is performed in the

code, such as an error prompt.

In the example on the right, the first string

variable is designated (Ninja), then a second is

created ( Art)note the space before Art

shows up in the printed resultand these two

strings are combined in the print function.

Lists


14/15

Lists Lists are the Python equivalent of what arrays are

in many other languages. They are declared like

variables, but allow the programmer to store

multiple values inside of one variable. These

variables have indexes, which can be used to

find data inside of the structure.

The syntax for a basic list is as follows:listName = [x, y, z, and so on]

As mentioned, the values for x, y, z are stored at

an index, which begins at 0 and counts upward,so x is stored at index 0, y at index 1, z at index 2,

and so on.

The example on the right uses the FOR loop to

cycle through the indexes, just as it would a set of

numbers in a given range.

Tuples


15/15

Tuples Tuples are identical to lists, with one important

distinction: a tuple cannot be changed once it is

declared. This may seem an arbitrary difference

since you, the programmer, can simply make a list

and not change it. However, a tuple is designed toprevent errors and bugs from altering sensitive data.

You may use a tuple to store constants (values that

arent subject to change like variables). For example,

you may want to store values that arent subject to

change (like sales tax, or vacation accrual rate) and

keep them separate from values that do (like sale

price or hours worked)

Note that a tuple uses parenthesis ( ) in its

declaration instead of brackets [ ], and that the

interpreter produced an error message when I tried

to change a value using the append function.

Translation:1) For warriorList, I was able to use the ap

Rogue to the end of the three I alread

replaced an item by specifying the inde

placed it at the end)

2) For warriorTuple, an error message wa

program rejected my attempt to chang

tuple object has no such function.

Documents

A Beginner’s Guide to Python Programming