City University of New York (CUNY) City University of New York (CUNY)
CUNY Academic Works CUNY Academic Works
Open Educational Resources Bronx Community College
2019
Python input output Python input output
Natalia Novak
CUNY Bronx Community College
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Topics to be discussed
Development Environment
Basic input and output
Variables and assignments
Python expressions
Division and modulo
Math module
Development Environment
Code development is usually done with an Integrated
Development Environment, or IDE.
There are various IDEs, we will be using the official Python
IDE that is distributed with the installation of Python, called
IDLE.
Development Environment
Demonstrate IDLE
Discuss Python Interpreter
Discuss Python Shell (line prompt, …)
Discuss File Editor (python files have extension .py)
My first program
In Python shell:
My first program
In IDLE’s file editor:
Then press F5 or go to Run → Run Module
Then check what you see in Python shell...
Save the program (File → Save) as a file named helloWorld.py
My second program
Create a new file (File → New File) and
type in the following:
# this is my second program!
print(" *")
print(" * | *")
print(" \\*/")
print("*-***-*")
print(" /*\\")
print(" * | *")
print(" *")
print("Do you like my snowflake?")
Save the program (File → Save) as mySecondProgram.py
Then press F5 or go to Run → Run Module
Then check what you see in Python shell...
Comment:
denotes one space
(whitespace)
# this is my second program!
print(" *")
print(" * | *")
print(" \\*/")
print("*-***-*")
print(" /*\\")
print(" * | *")
print(" *")
print("Do you like my snowflake?")
My second program
comment
(starts with #)
print() method displays
variables or expression values
Each print statement will output on a new line,
unless directed otherwise by a previous print statement
text enclosed in
quotes is known as
a string literal
In-class practice:
In the Python shell type in the following commands/
instructions (after each instruction, hit Enter key) and
observe the result:
>>> print("4")
>>> print(4)
>>> print("Alexa")
>>> print(Alexa)
>>> print("3"*5)
>>> print(3*5)
>>> print("2*8=",2*8)
In-class practice (continues):
In the Python shell type in the following commands/
instructions (after each instruction, hit Enter key) and
observe the result:
>>> name ="Peter"
>>> print("Hello",name)
>>> print("Hello",name,", how are you?")
>>> print("Hello",name,", how are you?)
>>> x = 8
>>> y = 20
>>> print(x*y)
In-class practice (continues):
In the Python shell type in the following commands/
instructions (after each instruction, hit Enter key) and
observe the result:
>>> print("Hello, \t how are you?")
>>> print("Hello! \n It is hot today, isn’t it?")
>>> print("\")
>>> print("\\")
>>> print("\\"*10)
>>> print("\\ "*10)
My third program
Create a new file (File → New File) and
type in the following:
# this is my third program!
name = input("Enter your name, please:")
print("*"*40)
print("Nice to meet you,",name,"!")
print("The weather is wonderful today,
isn't it?")
print("*"*40)
Save the program (File → Save) as myThirdProgram.py
Then press F5 or go to Run → Run Module
Then check what you see in Python shell...
My third program
Create a new file (File → New File) and
type in the following:
# this is my third program!
name = input("Enter your name, please:")
print("*"*40)
print("Nice to meet you,",name,"!")
print("The weather is wonderful today,
isn't it?")
print("*"*40)
Save the program (File → Save) as myThirdProgram.py
Then press F5 or go to Run → Run Module
Then check what you see in Python shell...
variable
(named reference where
the information is stored)
input() function/method
will read text entered by
the user, and assign the
entered text to the
name variable
Programs and terminology
A computer program mostly consists of a series of
commands/instructions, called statements.
Each statement usually appears on its own line.
In a program we can see:
expressions (code that return a value when evaluated)
x * 5
assignment statements (using the = symbol)
y = x * 5
print() statements (displays variables, or expression
values, or string literals)
print(“My name is”,name)
and many other things we will learn later
My fourth program
Visit our web-site:
go to ... page
scroll down to the date ...
right click on the myFourthProgram.py
choose Save link as ...
navigate to Documents folder, click on Save button
My fourth program
Go over the program
Variables and Assignments
Consider the following code fragment:
x = 10
y = x+2
z = x-y
x = 5
variables
(identifiers,
names)
assignment
statements
An identifier (name), is a sequence of letters
(a-z, A-Z), underscores (_), and digits (0-9),
and must start with a letter or an underscore.
Python is case sensitive, meaning upper and
lower case letters differ.
myFriendsName _counter n4
4toGo it’s $hk pl-7h
Variables, Assignments and Objects
Consider the following code fragment:
x = 10
y = x+2
z = x-y
x = 5
x
10
Variables, Assignments and Objects
Consider the following code fragment:
x = 10
y = x+2
z = x-y
x = 5
x
10
y
12
Variables, Assignments and Objects
Consider the following code fragment:
x = 10
y = x+2
z = x-y
x = 5
x
10
y
12
z
-2
Variables, Assignments and Objects
Consider the following code fragment:
x = 10
y = x+2
z = x-y
x = 5
x
10
y
12
z
-2
5
Variables, Assignments and Objects
Consider the following assignment statements:
Abra = x + 2
y + 2 = 17
2 = x-3
summ34_iuy = x+y+z+t
zebra = “blue”
x = x + 6
5*x = 15 * y
Which ones of them are valid assignment statements?
Variables, Assignments and Objects
Consider the following assignment statements:
Abra = x + 2
y + 2 = 17
2 = x-3
summ34_iuy = x+y+z+t
zebra = “blue”
x = x + 6
5*x = 15 * y
Which ones of them are valid assignment statements?
Data types
By now we saw three types of data:
integers 1, 4, -16
real numbers 1.2, -1.8, 0.54
(floating-point numbers)
strings “Peter”, “Hello, how are you?”
Python has built-in function that allows us to get the type of
an object: type()
Data types
By now we saw three types of data:
integers 1, 4, -16
real numbers 1.2, -1.8, 0.54
(floating-point numbers)
strings “Peter”, “Hello, how are you?”
Python has built-in function that allows us to get the type of
an object: type()
int
float
string
In-class practice:
In the Python shell type in the following assignment
statements and instructions and observe the result:
>>> name ="Peter"
>>> type(name)
>>> x = 287
>>> type(x)
>>> x = chr(x)
>>> type(x)
>>> y = 2.87
>>> type(y)
We will see later in the course the examples when this built-in
function is useful.
the built-in function
chr() converts from
integer to string
Arithmetic Expressions
We would like to be able to work with algebraic expressions
such as
2x+5 or 3x
2
-6y
3
+1 or ….
x− y
x+2
Arithmetic operator Description Python operator
+ addition
x+5
+
multiplication
2a
*
multiplication
a7
/
- subtraction
x-10
-
x
2
exponent x
2
**
Arithmetic Expressions
let’s see some conversions from math to Python:
x− y
x+2
Algebraic expression in math Algebraic expression in
Python
2x+5
2*x+5
3x
2
-6y
3
+1
3*x*x-6*y**3+1
(a+b+c) 3
(a+b+c)/3
y-2(x+9)
y-2*(x+9)
x
8
x**8
(x-y)/(x+2)
In-class practice:
In the Python File Editor finish the program (follow the
comments):
a = int(input(“Enter an integer value:”))
b = int(input(“Enter another integer value:”)
C = int(input(“Enter the last integer value:”)
# find the average of a,b, and c
# and display it
# find the product of a,b, and c and store
# the result in variable z
Python expressions
my_pay = base_pay + overtimeRate * numberOfHours
my_pay = base_pay + overtimeRate * numberOfHours
my_pay=base_pay+overtimeRate*numberOfHours
- may be it is a little bit less “readable”?
Python expressions
my_pay = base_pay + overtimeRate * numberOfHours
my_pay = base_pay + overtimeRate * numberOfHours
my_pay=base_pay+overtimeRate*numberOfHours
- may be it is a little bit less “readable”?
Python expressions
No commas in numbers!
1,876,904.76
Python expressions
No commas in numbers!
1,876,904.76 1876904.76
Python expressions
No commas in numbers!
1,876,904.76 1876904.76
We have compound operators!
x = x + 1 x += 1
n = n *100 n *= 100
a = a – 7 a -= 7
k = k / 5 k /= 5
Division and modulo
The division operator / performs division and returns a
floating-point number.
Examples:
>>> 40 / 5
8.0
>>> 8 / 10
0.8
Division and modulo
The quotient of the division can be found using the floored
division operator //
The resulting value is an integer type if both operands are
integers; if either operand is a float, then a float is returned.
Examples:
>>> 4 // 5
0
>>> 4.0 // 5.0
0.0
>>> 8.0 // 5.0
1.0
Division and modulo
The modulo operator (%) evaluates the remainder of the
division of two integer operands.
Examples:
56 % 10 is 6. Reason: 5 tens fit into 56, 6 is left (reminder)
9 % 9 is 0. Reason: 1 nine fits into 9, nothing is left
5 % 2 is 1. Reason: 2 twos fit into 5, 1 is left (remainder)
>>> 56 % 10
6
>>> 9%9
0
>>> 5 % 2
1
In-class practice
In the Python shell type in the following commands/
instructions (after each instruction, hit Enter key) and
observe the result, then do the assignment:
>>> my_age = 192
>>> his_age = 827
>>> my_age += his_age
>>> my_age
>>> his_age
Stop! Think: What happened there?
Next: type in a print statement that will display:
“I’m … years old and he is … years old”
In the … space should be displayed the values of my_age
and his_age variables.
In-class practice
Create a new file (File → New File), save it as qr.py and
write a program that does the following:
1) gets two numbers from the user (x and d) – use input()
2) Finds the quotient and remainder of the division x d
3) Displays the division, the quotient and the remainder of
the division – use print()
Then press F5 or go to Run → Run Module
Then check what you see in Python shell...
Here is how it might look in the Python shell when the
program is run:
Enter the dividend: 18
Enter the divisor: 7
The quotient of 18 / 7 is 2 and the remainder is 4.
Math module
While basic math operations like + or * are sufficient for
some computations, programmers sometimes wish to
perform more advanced math operations such as
computing a square root.
Python comes with a standard math module to support
such advanced math operations.
A module is Python code located in another file. The
programmer can import the module for use in their own
file, or in an interactive interpreter.
Math module
The programmer can import the module for use inan
interactive interpreter (Python shell)
>>> import math
>>> math.sqrt(9)
3.0
>>> math.factorial(4)
24
>>> math.pi
3.141592653589793
sqrt()
is a square root
function
factorial(4) =
1 2 3 4 = 24
pi is a
constant ()
Math module
The programmer can import the module for use inan
interactive interpreter (Python shell)
>>> import math
>>> math.sqrt(9)
3.0
>>> math.factorial(4)
24
>>> math.pi
3.141592653589793
function call
function call
constant
Math module
The programmer can import the module for use inan
interactive interpreter (Python shell)
>>> import math *
>>> sqrt(9)
3.0
>>> factorial(4)
24
>>> pi
3.141592653589793
Math module
I can also use Python File Editor: type in the program, save
it and run it!
import math
radius = float(input("please enter the
radius of a circle:"))
C = 2 * math.pi * radius # circumference
A = math.pi * radius ** 2 # area
print("The circumference of the circle of
radius",radius,"is",C)
print("The area of the circle of
radius",radius,"is",A)
Go to our web-site (Notices page) – download file circleMath.py
This OER material was produced as a result of the CS04ALL CUNY OER project.
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