Course a201 introduction to programming
This presentation is the property of its rightful owner.
Sponsored Links
1 / 27

Course A201: Introduction to Programming PowerPoint PPT Presentation


  • 73 Views
  • Uploaded on
  • Presentation posted in: General

Course A201: Introduction to Programming. 09/30/2010. 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

Download Presentation

Course A201: Introduction to Programming

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Course A201:Introduction to Programming

09/30/2010


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-2


for loops vs while loops

number = 1

While number< 11:

print(number)

count += 1

number_list = range(1, 11, 1)

for number innumber_list:

print(number)

  • The output will be exactly the same


Function range()

[functions]

  • input1, input2, input3, …

  • You give me some inputs

I am a function.

I will perform a certain job.

  • I give you some outputs back, explicitly or implicitly

  • output1, output2, output3, …


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!


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.


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

  • The 3rd argument is the ‘step argument’. The default value is 1.

  • Empty!


For loops

name = “Linger Xu”

foraain name:

print(aa)

number_list = range(-10, 1)

for number innumber_list:

print(number)


Python membership operator: in

  • The variable name is a string, “Linger Xu”

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

  • The variable number_list contains a list of numbers: [for number innumber_list ] fetch every number in this list sequentially, and put it into number

  • Go throught every member of a specified sequence:

  • -10, -9, -8, …


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 in


Python membership operator: in

  • The variable after in must be holding a sequence of values, such as string and list.

    number_list = 9

    for number innumber_list:

    print(number)

    ERROR! 'int' object is not iterable


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.


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 7

    1 2 3 4 5 6 7


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!!


Write nested for loops

  • What will happen if you indent the second print also?

    row_size = 5

    column_size = 7

    for row in range(row_size):

    for column in range(column_size ):

    print(column+1, end=“ ”)

    print()


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


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 row


Write nested for loops

  • Finish second problem in Part1 , Assignment 4

    Scalable Patterns: What do the following codes print?

  • Understand the 1st problem in Part2


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!


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])


String: Indexing

  • Count the occurrence of one letter in a string

    str1=“killer rabbit”

    target =“i”

    count = 0

    for letter in str1:

    if letter == target:

    count += 1

    print(“There’re ” + str(count) + “ ‘i‘s in string: ” + str(str1) )


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)

    4


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.”


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)


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)


String: Indexing and slicing

  • Understand the 2nd and 3rd problem in Part2


  • Have a nice evening!

  • See you tomorrow~


  • Login