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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

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Course a201 introduction to programming

Course A201:Introduction to Programming

09/30/2010


Outlines for this week
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
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
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 range1
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 range2
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 range3
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
For loops

name = “Linger Xu”

foraain name:

print(aa)

number_list = range(-10, 1)

for number innumber_list:

print(number)


Python membership operator in
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 in1
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 in2
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 loops1
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
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 loops1
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 loops2
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 loops3
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 loops4
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 loops5
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
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 indexing1
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 indexing2
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
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
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 methods1
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
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
String: Indexing and slicing

  • Understand the 2nd and 3rd problem in Part2



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