Introduction to Python Programming Concepts and Basics
Course A201:
Introduction to Programming
09/16/2010
Outlines for today
•
A new type of value: Boolean
•
Concept of keyword and indentation
•
Several basic concepts about Branching
–
IF - ELSE – IF and WHILE loop
•
Keep trace: what’s the stop condition
•
How and when to use “break” and “continue”
•
Demonstration of “Guess My Number Game”
Boolean and Comparison Operators
•
Boolean values:
True
or
False
•
Statements that will generate boolean values:
1 == 1
True
2 <= 0
False
4 > 1
True
9 != 99
True
“1”
== 1
False
These are Comparison
operators
keyword
•
In Assignment 1, question 2, the last variable is
“
for
”, which seams legit but actually not
This is a
KEYWORD
•
Keywords are a set of words that have
special/predefined meanings:
for
,
if
,
else
,
while
,
break
,
import
,
from
They will appear in orange in .py files in IDLE.
Indentation
•
In Python, proper indentations
are crucial ->
•
Python use indentations to
determine the structure of if-
else blocks, while blocks, etc.
•
If you forget to have
indentations, it will give you
syntax error
•
Enter tab
if user ==
“bye”
:
print (
“bye!”
)
elif user == “hi”:
print(
“Hi”
)
else:
print(
“…”
)
Conditional: IF
if user ==
“bye”
:
print (
“bye!”
)
elif user == “hi”:
print(
“Hi”
)
else:
print(
“…”
)
•
Don’t forget the COLON
•
You
can have only IF, or IF-
ELSE, or IF-ELIF, or IF-ELIF-
ELSE
•
You
can have another IF
block inside a IF block:
if …:
if …:
some statements
Conditional: WHILE
gpa = 0.0
while gpa <= 4.0:
gpa = float(raw_input(
“Enter GPA: ”
))
print(
“Not high enough”
)
•
While [
this condition
] is true, keep executing the
[
statements in here
]
•
Creating loops, make repetitive tasks easier
Keep trace
•
What’s wrong with this program:
health = 10
trolls = 0
damage = 3
while health != 0:
trolls += 1
health -= damage
Keep trace
Health
trolls
damage
health!= 0
10
0
3
True
7
1
3
True
4
2
3
True
1
3
3
True
-2
4
3
True
-5
5
3
True
-7
6
3
True
Keep trace
•
What’s wrong with this program:
health = 10
trolls = 0
damage = 3
while health != 0:
trolls += 1
health -= damage
<- This condition wil
l be true
FOREVER!!!
Keep trace
•
What’s wrong with this program:
health = 10
trolls = 0
damage = 3
while health
>
0:
trolls += 1
health -= damage
<- You
have to confirm that this
condition will be false at some
time
Usage of break
gpa = 0.0
while
True
:
gpa = float(raw_input(
“Enter GPA: ”
))
if gpa > 4.0:
break
•
Break out of the loop
Usage of continue
counter = 0
while counter <= 10:
count += counter
if count == 5
continue
print(counter)
print(“-” * 20)
•
The output won’t include 5.
When you reach continue,
the
rest of code (
in the red
rectangle
) will be omitted,
computer goes straight to nex
t
interation.
Guess My Number Game
•
pick a random number
•
while the player hasn't guessed the number,
let the player guess
•
If guess is right, congratulate the player
Lab work
•
Write a program that flips a coin 100 times
and then tells you the number of head and
tails
•
Modify your program so that it prompts the
user for the number of times to flip the coin
•
On paper in English first, on computer in
Python next
•
Optional team work
Have a nice evening
!
See you tomorrow~
Explore the fundamentals of Python programming with topics covering Boolean values, comparison operators, keywords, indentation rules, conditional statements (IF, WHILE), and keep-trace scenarios in code implementation. Understanding these concepts is essential for beginners in programming.
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Presentation Transcript
Course A201: Introduction to Programming 09/16/2010
Outlines for today A new type of value: Boolean Concept of keyword and indentation Several basic concepts about Branching IF - ELSE IF and WHILE loop Keep trace: what s the stop condition How and when to use break and continue Demonstration of Guess My Number Game
Boolean and Comparison Operators Boolean values: True or False Statements that will generate boolean values: 1 == 1 True 2 <= 0 False 4 > 1 True 9 != 99 True 1 == 1 False These are Comparison operators
keyword In Assignment 1, question 2, the last variable is for , which seams legit but actually not This is a KEYWORD Keywords are a set of words that have special/predefined meanings: for, if, else, while, break, import, from They will appear in orange in .py files in IDLE.
Indentation In Python, proper indentations are crucial -> Python use indentations to determine the structure of if- else blocks, while blocks, etc. If you forget to have indentations, it will give you syntax error Enter tab if user == bye : print ( bye! ) elif user == hi : print( Hi ) else: print( )
Conditional: IF if user == bye : print ( bye! ) elif user == hi : print( Hi ) else: print( ) Don t forget the COLON You can have only IF, or IF- ELSE, or IF-ELIF, or IF-ELIF- ELSE You can have another IF block inside a IF block: if : if : some statements
Conditional: WHILE gpa = 0.0 while gpa <= 4.0: gpa = float(raw_input( Enter GPA: )) print( Not high enough ) While [this condition] is true, keep executing the [statements in here] Creating loops, make repetitive tasks easier
Keep trace What s wrong with this program: health = 10 trolls = 0 damage = 3 while health != 0: trolls += 1 health -= damage
Keep trace Health 10 7 4 1 -2 -5 -7 trolls 0 1 2 3 4 5 6 damage 3 3 3 3 3 3 3 health!= 0 True True True True True True True
Keep trace What s wrong with this program: health = 10 trolls = 0 damage = 3 while health != 0: trolls += 1 health -= damage <- This condition will be true FOREVER!!!
Keep trace What s wrong with this program: health = 10 trolls = 0 damage = 3 while health > 0: trolls += 1 health -= damage <- You have to confirm that this condition will be false at some time
Usage of break gpa = 0.0 while True: gpa = float(raw_input( Enter GPA: )) if gpa > 4.0: break Break out of the loop
Usage of continue counter = 0 while counter <= 10: count += counter if count == 5 continue print(counter) print( - * 20) When you reach continue, the rest of code (in the red rectangle) will be omitted, computer goes straight to next interation. The output won t include 5.
Guess My Number Game pick a random number while the player hasn't guessed the number, let the player guess If guess is right, congratulate the player
Lab work Write a program that flips a coin 100 times and then tells you the number of head and tails Modify your program so that it prompts the user for the number of times to flip the coin On paper in English first, on computer in Python next Optional team work
Have a nice evening! See you tomorrow~
