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8/12/2019 A Beginners Guide to Python Programming
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A Beginners Guide to Pyth
Python Version: 3.3.4
8/12/2019 A Beginners Guide to Python Programming
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Contents
For Starters (IDLE)
Hello World!
Variables Operators
The IF statement
ElseIF and Else
Functions
Arguments For Loop
While Loop
Strings
Lists
Tuples
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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
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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.
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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)
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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
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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
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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 (
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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
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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
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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
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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
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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
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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
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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.
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