For迴圈的結構：首先是一個for，然後是一個可以用於存放各個元素的變數，經常用i，j，k表示計數器變數，接下來是in，然後是要遍歷的序列，然後是一個冒號，最後是另起一行加Tab製表符的迴圈體。for迴圈會按順序為序列中的每個元素執行一次迴圈體，當到達序列的末尾時，迴圈就結束了。用於存放元素的計數器變數如果在迴圈之前還不存在的話，也是會被直接建立的，並且計數器變數在迴圈體中也不一定會被使用到。舉例子如下：

for i in "python":
    print(i)

會發現它把各個字元都列印在不同的行，我想把它們列印在一行，怎麼辦呢？

for letter in "Trouble"
 
:
    print(letter,end = " ")

此時，它們就會老老實實地待在一起了，要是嫌捱得不夠近，可以把end後面雙引號裡面的空格刪除，它們就會變成”trouble”了。end=” “的意思是自己指定結束形式，也就是列印完計算機不要以回車結束，而是以空格結束。
接下來給出一個for迴圈和range()函式結合的一個小程式：

print("I'll show you 20 numbers between 1 and 20:\n")
for i in range(1,21):
           print(i,end = " ")
print("\n\nIn range 20,show the numbers every 2 numbers:\n"
 
)
for i in range(1,21,2):
           print(i,end = " ")
print("\n\nCounting the numbers between 1 and 10 backwards:\n")
for i in range(10,0,-1):
           print(i,end = " ")

上面程式裡面的迴圈序列是由range()函式給出的，該函式只在有需要的時候才會返回序列中的下一個值，如果給range()函式提供一個正整數，那就可以返回從零開始到給定數值（不包括它）的整數序列，如果給函式三個值，那麼這三個值會分別作為起始點，結束點和計數單位，起始點是始終都會得到的值，而結束點卻不包括在內。

Python提供了許多實用的函式和運算子，來操作包括字串在內的各種序列。這些運算子和函式可以告訴你一些有關序列的簡單而重要的資訊，比如長度和是否含有特定元素。比如：

information = input("\nEnter a word that you want to know something about:\n")
length = len(information)
print("\nThe length of your information is :",length)
print("\nThe most beautiful letter I think in the English language 's'",end=" ")
if "s" in information:
           print("is in your information")
else:
           print("is not in your information.")

input("\nEnter the enter key to exit!")

其中用到了len()函式，它會對傳給它的序列，返回該序列長度的響應。序列的長度包括它包含元素的數量，包括空格，感嘆號之類的元素。
還用到了in運算子，在判斷某個元素是否包含在某個序列時，可以用in。

下面貼出過去別人經常玩的一個Word Jumble遊戲：

新的個性化遊戲規則我限定如下：遊戲開始時，遊戲者有權決定要不要進入遊戲。遊戲者需要從計算機給出的打亂的字母中猜中原來的單詞是什麼，遊戲者只有5次機會猜中它，否則遊戲會重新給出一個新的打亂字母順序的單詞去猜，當然此時遊戲者可以選擇退出遊戲。

#Word Jumble
print("I am so happy that you can play this Word Jumble game with me!")
print("I'll give you a word that is scrambled.Your task is to unscramble it!")
print("And show me the right answer.")
yourwill = input("Do you accept this challenge?Yes or No:")
import random
WORDLIB = ('technique','architecture','heritage','gorgeous','fabulous','tremendous','application','heterostructure','electroluminescence','phosphorene','intriguing')

if yourwill.lower() == 'yes':

           input("Press the enter key to start!")
           while yourwill.lower() == 'yes':
                      counts = 1
                      word = random.choice(WORDLIB)
                      answer = word
                      newword = ''
                      while word:
                                 position = random.randint(0,len(word) - 1)
                                 if word:
                                            newword += word[position]
                                            print(word[position],end = " ")
                                            word = word[:position] + word[(position+1):]                      
                      yourguess = input("\nPlease enter your answer:")
                      while yourguess != answer and ((counts % 5) != 0):
                                 print("\nWrong!Guess it again!")
                                 yourguess = input("\nPlease change your answer:")
                                 counts += 1
                      if yourguess == answer:
                                 print("\nCongratulation!You made it.The answer is",answer)
                      else:
                                 print("\nI'm sorry.The answer is",answer)
                      yourwill = input("\nWant to challenge it again?Yes or No:")
           print("\nLooking forward to your next visiting!")
else:
           print("\nLooking forward to your next visiting!")
input("\n Enter the enter key to withdraw!")

編寫這個遊戲之前，我們要理解字串及元組的不變性，能通過“+”運算子建立新的字串及用“”+“”運算子連線其他元組成新的元組，理解切片的概念，會建立元組並會對其切片和索引。
注意：Python中常量一般全大寫，但這只是約定俗成的東西，Python並不會阻止你用非大寫的名字做常量，只是靠自覺。

其實可以將上面while迴圈改成for迴圈。你可以嘗試一下。核心如下：

import random
WORDLIB = ("mood","happy","young")
answer = random.choice(WORDLIB)
newword = answer
word = ''
for i in range(len(answer)):
           position = random.randint(0,len(newword)-1)
           word += newword[position]
           newword = newword[0:position]+newword[(position+1):]
print(answer,'is scrambled to',word) 

Word Jumble升級版：加入了計分和提示。限制5次機會去贏得遊戲，並在遊戲者遇到困難時詢問要不要給提示。

#Word Jumble升級版
print("I am so happy that you can play this Word Jumble game with me!")
print("I'll give you a word that is scrambled.Your task is to unscramble it!")
print("And show me the right answer.")
yourwill = input("Do you accept this challenge?Yes or No:")
import random
WORDLIB = ('technique','architecture','heritage','gorgeous','fabulous','tremendous','application','heterostructure','electroluminescence','phosphorene','intriguing')

if yourwill.lower() == 'yes':

           input("Press the enter key to start!")
           while yourwill.lower() == 'yes':
                      hinttimes = 1
                      counts = 1
                      word = random.choice(WORDLIB)
                      answer = word
                      newword = ''
                      while word:
                                 position = random.randint(0,len(word) - 1)
                                 if word:
                                            newword += word[position]
                                            print(word[position],end = " ")
                                            word = word[:position] + word[(position+1):]                      
                      yourguess = input("\nPlease enter your answer:")
                      while yourguess != answer and ((counts % 5) != 0):
                                 print("\nWrong!Guess it again!")
                                 if counts > 3 and hinttimes == 1:
                                            hint = input("Want a hint?Yes or No:")
                                            if hint.lower() == 'yes':
                                                       print("\nThe first letter is",answer[0])
                                                       yourguess = input("\nPlease give your new answer:")
                                                       counts += 1
                                                       hinttimes = 0
                                            else:
                                                       yourguess = input("\nPlease give your new answer:")
                                                       counts += 1
                                 else:
                                            yourguess = input("\nPlease go on to guess the answer:")
                                            counts += 1
                      if yourguess == answer:
                                 if hinttimes == 0:
                                            print("\nCongratulation!You made it.The answer is",answer,".Finally the score you have got is",(6-counts)*20-10,"points!")
                                 else:
                                            print("\nCongratulation!You made it.The answer is",answer,".Finally the score you have got is",(6-counts)*20,"points!")           
                      else:
                                 print("\nI'm sorry.The answer is",answer,".Finally the score you have got is 0 point!")
                      yourwill = input("\nWant to challenge it again?Yes or No:")
           print("\nLooking forward to your next visiting!")
else:
           print("\nLooking forward to your next visiting!")
input("\n Enter the enter key to withdraw!")

小程式：獲取使用者輸入的一條資訊，將其倒序輸出

info = input("Enter a information that I will inverse it to you:")
inverse = ''
for i in range(len(info)-1,-1,-1):
           inverse += info[i]
print(inverse)

計算機與使用者之間的小猜字遊戲：

import random
LIB = ("kid","wild","elegant")
word = random.choice(LIB)
print("I have randomly chose a word,can you guess it?The lenght of the word is",len(word))
print("\nYou only have 5 chances to ask me if there is some letter in it. ")
print("\nAnd I only can just say yes or no.")
chance = 1
while chance <= 5:
           letter = input("\nTell me the letter you want to ask:")
           if letter in word:
                      print("\nYes")
                      chance += 1
           else:
                      print("\nNo")
                      chance += 1
answer = input("\nNow tell me the word you guess:")
if answer.lower() == word:
           print("\nYou are right!The word is",word,"!")
else:
           print("\nSorry!The word is",word,"!")

加一個小題：輸出1到5000的所有的5和7的公因數，要求每20個列印成一行。

j = 0
for i in range(1,5000):
           if i % 5 == 0 and i % 7 == 0:
                      print(i,end = ' ')
                      j += 1
           if j != 0 and j % 20 == 0:
                      print("\n")
                      j = 0