面向非程式設計師的 Python 3 教程/列表
您已經看到了儲存單個值的普通變數。但是，其他變數型別可以儲存多個值。它們被稱為容器，因為它們可以包含多個物件。最簡單的型別稱為列表。以下是一個使用列表的示例
which_one = int(input("What month (1-12)? "))
months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
if 1 <= which_one <= 12:
print("The month is", months[which_one - 1])
以及一個輸出示例
What month (1-12)? 3 The month is March
在本例中，months 是一個列表。months 使用 months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 和 'August', 'September', 'October', 'November', 'December'] 行定義（請注意，\ 也可以用於分割長行，但在這種情況下，Python 足夠智慧，能夠識別出括號內的所有內容都屬於一起）。[ 和 ] 用逗號 (,) 分隔列表項，開始和結束列表。列表在 months[which_one - 1] 中使用。列表由從 0 開始編號的項組成。換句話說，如果您想要 January，則應使用 months[0]。給列表一個數字，它將返回儲存在該位置的值。
語句 if 1 <= which_one <= 12: 僅在 which_one 包含在 1 到 12 之間時才為真（換句話說，如果您在代數中見過，它就是您所期望的）。
列表可以被認為是一系列盒子。每個盒子都有不同的值。例如，由 demolist = ['life', 42, 'the universe', 6, 'and', 9] 建立的盒子將如下所示
| 盒子編號 | 0 | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|---|
| demolist | "life" | 42 | "the universe" | 6 | "and" | 9 |
每個盒子都由其編號引用，因此語句 demolist[0] 將獲取 'life'，demolist[1] 將獲取 42，依此類推，直到 demolist[5] 獲取 9。
下一個示例只是為了展示列表可以做的很多其他事情（就這一次而言，我不希望您輸入它，但您可能應該在互動模式下玩一下列表，直到您對它們感到滿意）。如下所示
demolist = ["life", 42, "the universe", 6, "and", 9]
print("demolist = ",demolist)
demolist.append("everything")
print("after 'everything' was appended demolist is now:")
print(demolist)
print("len(demolist) =", len(demolist))
print("demolist.index(42) =", demolist.index(42))
print("demolist[1] =", demolist[1])
# Next we will loop through the list
for c in range(len(demolist)):
print("demolist[", c, "] =", demolist[c])
del demolist[2]
print("After 'the universe' was removed demolist is now:")
print(demolist)
if "life" in demolist:
print("'life' was found in demolist")
else:
print("'life' was not found in demolist")
if "amoeba" in demolist:
print("'amoeba' was found in demolist")
if "amoeba" not in demolist:
print("'amoeba' was not found in demolist")
another_list = [42,7,0,123]
another_list.sort()
print("The sorted another_list is", another_list)
輸出為
demolist = ['life', 42, 'the universe', 6, 'and', 9] after 'everything' was appended demolist is now: ['life', 42, 'the universe', 6, 'and', 9, 'everything'] len(demolist) = 7 demolist.index(42) = 1 demolist[1] = 42 demolist[ 0 ] = life demolist[ 1 ] = 42 demolist[ 2 ] = the universe demolist[ 3 ] = 6 demolist[ 4 ] = and demolist[ 5 ] = 9 demolist[ 6 ] = everything After 'the universe' was removed demolist is now: ['life', 42, 6, 'and', 9, 'everything'] 'life' was found in demolist 'amoeba' was not found in demolist The sorted another_list is [0, 7, 42, 123]
此示例使用了一堆新函式。請注意，您可以直接 print 整個列表。接下來，append 函式用於將一個新項新增到列表的末尾。len 返回列表中包含的項數。列表的有效索引（如在 [] 內使用的數字）範圍為 0 到 len - 1。index 函式告訴項在列表中的第一個位置的位置。請注意 demolist.index(42) 如何返回 1，以及在執行 demolist[1] 時它如何返回 42。要獲取有關列表為其提供的所有函式的幫助，請在互動式 Python 直譯器中鍵入 help(list)。
行 # Next we will loop through the list 只是對程式設計師的提醒（也稱為註釋）。Python 會忽略當前行中 # 之後的所有內容。接下來，這些行
for c in range(len(demolist)):
print('demolist[', c, '] =', demolist[c])
建立一個變數 c，它從 0 開始，並不斷增加，直到達到列表的最後一個索引。同時，print 語句打印出列表中的每個元素。
執行上述操作的一種更好的方法是
for c, x in enumerate(demolist):
print("demolist[", c, "] =", x)
del 命令可用於從列表中刪除給定的元素。接下來的幾行使用 in 運算子來測試元素是否在列表中或不在列表中。sort 函式對列表進行排序。這在您需要按從小到大或按字母順序排列的列表時很有用。請注意，這會重新排列列表。總而言之，對於列表，將執行以下操作
| 示例 | 解釋 |
|---|---|
demolist[2]
|
訪問索引為 2 的元素 |
demolist[2] = 3
|
將索引為 2 的元素設定為 3 |
del demolist[2]
|
刪除索引為 2 的元素 |
len(demolist)
|
返回 demolist 的長度 |
"value" in demolist
|
如果"value"是 demolist 中的元素，則為 True |
"value" not in demolist
|
如果 "value" 不是 demolist 中的元素，則為 True |
another_list.sort()
|
對 another_list 進行排序。請注意，要排序的列表必須全部為數字或全部為字串。 |
demolist.index("value")
|
返回 "value" 首次出現的索引 |
demolist.append("value")
|
在列表的末尾新增元素 "value" |
demolist.remove("value")
|
從 demolist 中刪除 value 的第一次出現（與 del demolist[demolist.index("value")] 相同） |
下一個示例以更有用的方式使用這些功能
menu_item = 0
namelist = []
while menu_item != 9:
print("--------------------")
print("1. Print the list")
print("2. Add a name to the list")
print("3. Remove a name from the list")
print("4. Change an item in the list")
print("9. Quit")
menu_item = int(input("Pick an item from the menu: "))
if menu_item == 1:
current = 0
if len(namelist) > 0:
while current < len(namelist):
print(current, ".", namelist[current])
current = current + 1
else:
print("List is empty")
elif menu_item == 2:
name = input("Type in a name to add: ")
namelist.append(name)
elif menu_item == 3:
del_name = input("What name would you like to remove: ")
if del_name in namelist:
# namelist.remove(del_name) would work just as fine
item_number = namelist.index(del_name)
del namelist[item_number]
# The code above only removes the first occurrence of
# the name. The code below from Gerald removes all.
# while del_name in namelist:
# item_number = namelist.index(del_name)
# del namelist[item_number]
else:
print(del_name, "was not found")
elif menu_item == 4:
old_name = input("What name would you like to change: ")
if old_name in namelist:
item_number = namelist.index(old_name)
new_name = input("What is the new name: ")
namelist[item_number] = new_name
else:
print(old_name, "was not found")
print("Goodbye")
以下是部分輸出
-------------------- 1. Print the list 2. Add a name to the list 3. Remove a name from the list 4. Change an item in the list 9. Quit Pick an item from the menu: 2 Type in a name to add: Jack Pick an item from the menu: 2 Type in a name to add: Jill Pick an item from the menu: 1 0 . Jack 1 . Jill Pick an item from the menu: 3 What name would you like to remove: Jack Pick an item from the menu: 4 What name would you like to change: Jill What is the new name: Jill Peters Pick an item from the menu: 1 0 . Jill Peters Pick an item from the menu: 9 Goodbye
這是一個很長的程式。讓我們看一下原始碼。行 namelist = [] 使變數 namelist 成為一個沒有項（或元素）的列表。下一條重要的行是 while menu_item != 9:。此行啟動一個迴圈，允許該程式的菜單系統。接下來的幾行顯示選單並決定要執行程式的哪個部分。
部分
current = 0
if len(namelist) > 0:
while current < len(namelist):
print(current, ".", namelist[current])
current = current + 1
else:
print("List is empty")
遍歷列表並列印每個名稱。len(namelist) 告訴列表中有多少個項。如果 len 返回 0，則列表為空。
然後，在幾行之後，語句 namelist.append(name) 出現。它使用 append 函式在列表的末尾新增一項。再向下跳兩行，請注意以下程式碼段
item_number = namelist.index(del_name)
del namelist[item_number]
這裡，index 函式用於查詢將在稍後用於刪除該項的索引值。del namelist[item_number] 用於刪除列表中的一個元素。
接下來的部分
old_name = input("What name would you like to change: ")
if old_name in namelist:
item_number = namelist.index(old_name)
new_name = input("What is the new name: ")
namelist[item_number] = new_name
else:
print(old_name, "was not found")
使用 index 查詢 item_number，然後將 new_name 放在 old_name 的位置。
恭喜，掌握了列表，您現在對該語言的瞭解已經足夠了，可以進行計算機可以進行的任何計算（這在技術上被稱為 圖靈完備性）。當然，還有許多功能可以幫助您更輕鬆地完成工作。
test.py
## This program runs a test of knowledge
# First get the test questions
# Later this will be modified to use file io.
def get_questions():
# notice how the data is stored as a list of lists
return [["What color is the daytime sky on a clear day? ", "blue"],
["What is the answer to life, the universe and everything? ", "42"],
["What is a three letter word for mouse trap? ", "cat"]]
# This will test a single question
# it takes a single question in
# it returns True if the user typed the correct answer, otherwise False
def check_question(question_and_answer):
# extract the question and the answer from the list
# This function takes a list with two elements, a question and an answer.
question = question_and_answer[0]
answer = question_and_answer[1]
# give the question to the user
given_answer = input(question)
# compare the user's answer to the tester's answer
if answer == given_answer:
print("Correct")
return True
else:
print("Incorrect, correct was:", answer)
return False
# This will run through all the questions
def run_test(questions):
if len(questions) == 0:
print("No questions were given.")
# the return exits the function
return
index = 0
right = 0
while index < len(questions):
# Check the question
#Note that this is extracting a question and answer list from the list of lists.
if check_question(questions[index]):
right = right + 1
# go to the next question
index = index + 1
# notice the order of the computation, first multiply, then divide
print("You got", right * 100 / len(questions),\
"% right out of", len(questions))
# now let's get the questions from the get_questions function, and
# send the returned list of lists as an argument to the run_test function.
run_test(get_questions())
值 True 和 False 分別指向 1 和 0。它們通常用於健全性檢查、迴圈條件等。您將在稍後（第 布林表示式 章）瞭解有關此內容的更多資訊。請注意，get_questions() 本質上是一個列表，因為儘管它在技術上是一個函式，但返回一個列表的列表是它唯一的功能。
示例輸出
What color is the daytime sky on a clear day? green Incorrect, correct was: blue What is the answer to life, the universe and everything? 42 Correct What is a three letter word for mouse trap? cat Correct You got 66 % right out of 3
擴充套件 test.py 程式，使其包含一個選單，提供進行測試、檢視問題和答案列表以及退出選項。此外，新增一個新問題，問“真正先進的機器會發出什麼聲音？”，答案是“ping”。
解決方案
擴充套件 test.py 程式，使其包含一個選單，提供進行測試、檢視問題和答案列表以及退出選項。此外，新增一個新問題，問“真正先進的機器會發出什麼聲音？”，答案是“ping”。
## This program runs a test of knowledge
questions = [["What color is the daytime sky on a clear day? ", "blue"],
["What is the answer to life, the universe and everything? ", "42"],
["What is a three letter word for mouse trap? ", "cat"],
["What noise does a truly advanced machine make?", "ping"]]
# This will test a single question
# it takes a single question in
# it returns True if the user typed the correct answer, otherwise False
def check_question(question_and_answer):
# extract the question and the answer from the list
question = question_and_answer[0]
answer = question_and_answer[1]
# give the question to the user
given_answer = input(question)
# compare the user's answer to the testers answer
if answer == given_answer:
print("Correct")
return True
else:
print("Incorrect, correct was:", answer)
return False
# This will run through all the questions
def run_test(questions):
if len(questions) == 0:
print("No questions were given.")
# the return exits the function
return
index = 0
right = 0
while index < len(questions):
# Check the question
if check_question(questions[index]):
right = right + 1
# go to the next question
index = index + 1
# notice the order of the computation, first multiply, then divide
print("You got", right * 100 / len(questions),
"% right out of", len(questions))
#showing a list of questions and answers
def showquestions():
q = 0
while q < len(questions):
a = 0
print("Q:" , questions[q][a])
a = 1
print("A:" , questions[q][a])
q = q + 1
# now let's define the menu function
def menu():
print("-----------------")
print("Menu:")
print("1 - Take the test")
print("2 - View a list of questions and answers")
print("3 - View the menu")
print("5 - Quit")
print("-----------------")
choice = "3"
while choice != "5":
if choice == "1":
run_test(questions)
elif choice == "2":
showquestions()
elif choice == "3":
menu()
print()
choice = input("Choose your option from the menu above: ")