Course A201: - PowerPoint Presentation

Slide1

Course A201:Introduction to Programming

09/30/2010Slide2

Outlines for this week

How to write for loops

Function

range()

Python membership operator: in

Write nested for loops to print out certain shapes

More on Strings

String Indexing

Function

len

()

String functions

Finish Part-1, understand what to do in Part-2Slide3

for loops vs while loops

number = 1

While

number< 11:

print(number)

count += 1number_list = range(1, 11, 1)for number in number_list: print(number)

The output will be exactly

the sameSlide4

Function range()

[functions]

I am a function.

I will perform a certain job.

input1, input2, input3, …

output1, output2, output3, …

You give

me some inputs

I give you some outputs back, explicitly

or implicitlySlide5

Function range()

Example of how to use range():

>>> range()

ERROR! range expected at least 1 arguments

>>> range(10)

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]>>> ans = range(10)>>> ans[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

10 is not included!Slide6

Function range()

So, we know that range() will require at least one argument, let’s see how it works when there’re two:

>>> range(3, 11)

[3, 4, 5, 6, 7, 8, 9,10]

>>> range(-10,1)

[-10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0]>>> range(10,1)[]

Empty!

when second argument is smaller than the first one, and there is no third argument.Slide7

Function range()

Three arguments?

>>> range(3, 11, 2)

[3, 5, 7, 9]

>>> range(10, 1, -1)

[10, 9, 8, 7, 6, 5, 4, 3, 2] >>> range(-10, -1, -1)[]>>> range(2, 8, 0)ERROR! range() step argument must not be zero

Empty!

The 3

rd

argument

is the ‘step argument’. The default value is 1.Slide8

For loops

name =

“Linger

Xu

”

for aa in name: print(aa)number_list = range(-10, 1)

for number in

number_list: print(number)Slide9

Python membership operator: in

The variable

name

is a string,

“Linger

Xu” [for aa in name] fetch every letter in this string sequentially, and put it into aa

The variable number_list contains a list of numbers: [for number

in number_list ] fetch every number in this list sequentially, and put it into number

Go

throught

every

member

of a specified sequence:

-10, -9, -8, …Slide10

Python membership operator: in

user =

“5198”

if

“1”

in user: print(“Number 1 is in”, user) if “0” not in user: print(“Number 0 is not in”, user)

membership operator:

in / not inSlide11

Python membership operator: in

The variable after

in

must be holding a sequence of values, such as string and list.

number_list

= 9for number in number_list: print(number)ERROR! 'int

' object is not iterableSlide12

For loops

Finish first problem in Part1 , Assignment 4

Write a program that counts for the user using a for loop as shown in class. Let the user enter the starting number, the ending number, and the amount by which to count.Slide13

Write nested for loops

How to print out:

1 2 3 4 5 6 7

1 2 3 4 5 6 7

1 2 3 4 5 6 7

1 2 3 4 5 6 71 2 3 4 5 6 7Slide14

Write nested for loops

row_size

= 5

column_size

= 7

for row in range(row_size): for column in range(column_size ):

print(column+1, end=“ ”) print()

Loop within a loop. Look out for indentation!!Slide15

Write nested for loops

What will happen if you indent the second print also?

row_size

= 5

column_size

= 7for row in range(row_size): for column in

range(column_size ): print(column+1, end=“ ”)

print()Slide16

Write nested for loops

How to print out:

1 1 1 1 1 1 1

2 2 2 2 2 2 2

3 3 3 3 3 3 3

4 4 4 4 4 4 4 5 5 5 5 5 5 5 Slide17

Write nested for loops

row_size

= 5

column_size

= 7

for row in range(row_size): for column in range(column_size ):

print(row+1, end=“ ”) print()

Just change column in 5th

line to

rowSlide18

Write nested for loops

Finish second problem in Part1 , Assignment 4

Scalable Patterns: What do the following codes print?

Understand the 1

st problem in Part2 Slide19

String: Indexing

str

=

“killer rabbit”

Ex:

str[0] returns “k” str[1] returns “i” str[3] returns

“l” str[-3] returns “b”

str[-14] returns Error! Index out of range!

k

i

l

l

e

r

r

a

b

bit012

34

5

6

7

8

9

10

11

12

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1Slide20

String: Indexing

Try this program (in textbook Chapter 4):

import random

word = "index"

print("The word is: ", word, "\n“)

high = len(word)low = -len(word)for i in range(10): position = random.randrange(low, high) print("word[", position, "]\t", word[position])Slide21

String: Indexing

Count the occurrence of one letter in a string

str1=

“killer rabbit”

target =

“i”count = 0for letter in str1: if letter == target: count += 1print(“There’re ”

+ str(count) + “ ‘i‘s

in string: ” + str(str1) )Slide22

Function len()

Return an integer that represents how many elements are there in this specified sequence

>>> user = input(

“Type a word: “

)

>>> user = “I like Python.”>>> len(user)14>>> user = “5198”>>> len

(user)4Slide23

String: methods

quote =

"I like Python.“

quote.upper

() -> capitalize everything

–“I LIKE PYTHON.”quote.lower() -> small letter everything –“I like python.” quote.title() -> capitalize the first letter of every word –“I Like Python.”Slide24

String: methods

quote =

"I like Python.“

quote.strip

() -> removes spaces, tabs, newlines before and after

quote.replace(“like”, “dislike programming in”) –“I dislike programming in Python.”Try quote.center(50)Slide25

String methods vs Built-in functions

When you want to use a string method, you’ve got to use the

dot

“

.”:>>> quote = "I like Python.">>> quote.upper()'I LIKE PYTHON.'>>> upper(quote) <- Error!While built-in function>>>

len(quote)>>> range(10)Slide26

String: Indexing and slicing

Understand the 2

nd

and 3

rd

problem in Part2 Slide27

Have a nice evening

!

See you tomorrow~