Stanford Python程式課 - 第四週

第四週學習目標

• Lesson 10: List 清單
• Lesson 11: Text 文字

Code in Place 第四週課程 Lesson 10: Lists

Lesson 10: List 清單

學習重點

• 創建、修改清單 List
• 以迴圈方式存取清單元素 Loop over List

Mutable vs Immutable when Passed as Parameters

• Mutable: variables act like they are copied
• Immutable: variables act lie their URL is copied

Lesson 10 Lists: Mutable vs Immutable Variables

YouTube課程影片

   Lecture 10-1: Intro

   Lecture 10-2: Using the console

   Lecture 10-3: Lists

   Lecture 10-4: List functions

   Lecture 10-5: List looping

   Lecture 10-6: List as params

   Lecture 10-7: Average scores

點我下載課程講義

延伸閱讀Python Reader

   Python Lists

點我到 List 課程程式範例

Lesson 11: Text 文字

文字處理有很多令人驚訝的用途，例如研究人員跟醫生發現人類的基因組測序 (DNA sequence) 的問題可以將 DNA 當成字串來運算處理！

課程介紹的真實應用案例是非洲迦納的程式設計工程師 mPedigree 公司，利用手機簡訊回傳藥品包裝上的字串，透過金鑰確認是否為真藥或偽藥的問題，Python程式範例在文章最後。

Code in Place 範例：mPedigree 公司利用字串簡訊解決偽藥問題

學習重點

• 了解Python的字串
• 字串是 immutable
• 以迴圈處理字串、創建新字串

YouTube課程影片

   Lecture 11-1: Introduction

   Lecture 11-2: Revisiting Strings

   Lecture 11-3: Immutability

   Lecture 11-4: String Functions

   Lecture 11-5: String Processing

   Lecture 11-6: mPedigree Goldenkeys

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    String

點我到Text 程式範例

第一週課程

第二週課程

第三週課程

未完待續 ...

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List 程式範例

listexamples.py

"""
File: listexamples.py
---------------------
This program contains examples of using different functionality of
lists to show how you can do different list operations.
"""


def access_list_elements():
    """
    Shows an example of accessing individual elements in a list
    as well as overwriting a value.
    """
    num_list = [10, 20, 30, 40, 50]
    print('num_list =', num_list)
    print('num_list[0] =', num_list[0])
    print('num_list[1] =', num_list[1])
    print('Setting num_list[0] to 15')
    num_list[0] = 15
    print('num_list =', num_list)


def print_individual_list_elements():
    """
    Shows an example of using a for-loop with range to iterate
    through the elements of a list.
    """
    letters = ['a', 'b', 'c', 'd', 'e']
    print('letters =', letters)
    print('length of letters =', len(letters))
    for i in range(len(letters)):
        print(i, "->", letters[i])


def appending_elements():
    """
    Shows two examples of using appending elements onto lists.
    """
    alist = [10, 20, 30]
    print('alist =', alist)
    print('Appending 40 to alist')
    alist.append(40)
    print('Appending 50 to alist')
    alist.append(50)
    print('alist =', alist)

    new_list = []
    print('new_list =', new_list)
    print('Appending a to new_list')
    new_list.append('a')
    print('Appending 4.3 to new_list')
    new_list.append(4.3)
    print('new_list =', new_list)


def popping_elements():
    """
    Shows an example of popping elements off a list.
    """
    alist = [10, 20, 30, 40, 50]
    print('alist =', alist)
    x = alist.pop()
    print('popped element from alist, got', x)
    print('alist =', alist)
    x = alist.pop()
    print('popped element from alist, got', x)
    print('alist =', alist)
    x = alist.pop()
    print('popped element from alist, got', x)
    print('alist =', alist)
    x = alist.pop()
    print('popped element from alist, got', x)
    print('alist =', alist)
    x = alist.pop()
    print('popped element from alist, got', x)
    print('alist =', alist)


def look_up_elements():
    """
    Shows an example of using 'in' to check if a value is contained in
    a list.
    """
    str_list = ['Ruth', 'John', 'Sonia']
    print('str_list =', str_list)
    if 'Sonia' in str_list:
        print('Sonia is in str_list')


def for_each_loop():
    """
    Shows an example of using a for-each loop with a list.
    """
    str_list = ['Ruth', 'John', 'Sonia']
    for elem in str_list:
        print(elem)


def main():
    """
    We call a number of different functions that show the results
    of different list operations to show examples of how they work.
    """
    access_list_elements()
    print_individual_list_elements()
    appending_elements()
    popping_elements()
    look_up_elements()
    for_each_loop()


if __name__ == '__main__':
    main()

listparameter.py

"""
File: listparameter.py
---------------------
This program contains examples of using lists as parameters,
especially in different type of for loops.
"""


def add_five_buggy(alist):
    """
    Attempts to add 5 to all the elements in the list.
    BUGGY CODE!  Does not actually add 5 to the list elements
    if values are primitive type (like int or float), since
    value would just be a local copy of such variables.
    """
    for value in alist:
        value += 5


def add_five_working(alist):
    """
    Successfully adds 5 to all the elements in the list.
    Changes made to the list persist after this function ends
    since we are changing actual values in the list.
    """
    for i in range(len(alist)):
        alist[i] += 5


def create_new_list(alist):
    """
    Shows an example of what happens when you create a new list
    that has the same name as a parameter in a function.  After
    you create the new list, you are no longer referring to the
    parameter "alist" that was passed in
    """
    # This "alist" is referring to the parameter "alist"
    alist.append(9)

    # Creating a new "alist". This is not the same as the parameter
    # passed in.  After this line references to "alist" are no longer
    # referring to the parameter "alist" that was passed in.
    alist = [1, 2, 3]


def main():
    values = [5, 6, 7, 8]
    print('values =', values)

    add_five_buggy(values)
    print('values =', values)

    add_five_working(values)
    print('values =', values)

    values = [5, 6, 7, 8]
    create_new_list(values)
    print('values =', values)


if __name__ == '__main__':
    main()

averagescores.py

"""
File: averagescores.py
----------------------
This program reads score values from a user and computes their
average.  It also adds extra credit to all the scores and computes
the new average.
"""


EXTRA_CREDIT = 5


def get_scores():
    """
    Asks the user for a list of scores (numbers).
    Returns a list containing the scores
    """
    score_list = []
    while True:
        score = float(input("Enter score (0 to stop): "))
        if score == 0:
            break
        score_list.append(score)
    return score_list


def compute_average(score_list):
    """
    Returns the average value of the list of scores passed in.
    """
    num_scores = len(score_list)
    total = sum(score_list)
    return total / num_scores


def give_extra_credit(score_list, extra_credit_value):
    """
    Adds extra_credit_value to all the values in score_list.
    """
    for i in range(len(score_list)):
        score_list[i] += extra_credit_value


def print_list(alist):
    """
    Prints all the values in the list passed in
    """
    for value in alist:
        print(value)


def main():
    """
    Computes average for a set of scores entered by the user.
    Then adds extra credit to scores and recomputes average.
    """
    scores = get_scores()
    print("Scores are:")
    print_list(scores)
    avg = compute_average(scores)
    print('Average score is', avg)

    print('Adding extra credit:', EXTRA_CREDIT, "points")
    give_extra_credit(scores, EXTRA_CREDIT)
    print("New scores are:")
    print_list(scores)
    avg = compute_average(scores)
    print('New average is', avg)


if __name__ == '__main__':
    main()

Text 程式範例

goldkeys.py:

import random 

N_LABELS = 5000

def main():
	for i in range(N_LABELS):
		rand_part = pad(random.randint(0, 99999), 5)
		unique_part = pad(i, 4)
		id = rand_part + unique_part
		print(id)


def pad(num, length):
	"""
	>>> pad(42, 4)
	'0042'
	>>> pad(100, 3)
	'100'
	"""
	num_string = str(num)
	while len(num_string) < length:
		# insert a 0 at the start of the string, increasing its length by one
		num_string = "0" + num_string
	return num_string

if __name__ == "__main__":
	main()