摘要：表達式表達式是運算符和操作數所構成的序列運算符優先級同級的運算符的優先級還是有區別的比如邏輯運算符里的的優先級大于兩個括號同級，左結合出現賦值符號時，右結合優先級在文本文件中編寫代碼腳本是后綴名為的文件，通過命令行執行推薦的，大型工程適合用

表達式（Expression）是運算符（operator）和操作數（operand）所構成的序列

>>> 1 + 1
2
>>> a = [1,2,3]
>>> 1 + 1 + 1 + 1
4
>>> 1 + 2 * 3
7
>>> 1 * 2 + 3
5
>>> a = 1 + 2 * 3
>>> a = 1
>>> b = 2
>>> c = a and b or c
>>> c = int("1") + 2

同級的運算符的優先級還是有區別的 比如邏輯運算符里的and的優先級大于or

>>> a = 1
>>> b = 2
>>> c = 3
>>> a + b * c
7
>>> 1 or 2
1
>>> 1 and 3
3
>>> a or b and c
1
>>> a or (b and c)
1
>>> a or 3
1
>>> (a or b) and c
3
>>> (a or b) and (c + 1)   //兩個括號同級，左結合
4
>>> a = 1
>>> b = 2
>>> c = a + b    //出現賦值符號時，右結合
>>> print(c)    
3
>>> c = a or b
>>> print(c)
1
>>> a = 1
>>> b = 2
>>> c = 2
>>> not a or b + 2 == c
False
>>> ((not a) or ((b + 2) == c))    //優先級：not > and > or
False

python腳本是后綴名為.py的文件，通過命令行“python filename.py”執行

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單行注釋用#
多行注釋用```

主要有條件控制（if else）、循環控制（for while）、分支

# encoding: utf-8

mood = False

if mood :
    print("go to left")
    # print("back away")
# print("back away")
else :
    print("go to right")
    
a = 1
b = 2
c = 2
# if后面不僅可以是布爾值，還可以是表達式
if a or b + 1 == c :
    print("go to left")
    # print("back away")
# print("back away")
else :
    print("go to right")

# encoding: utf-8
"""
    一段小程序
"""
# constant 常量  建議全大寫
ACCOUNT = "hughie"
PASSWORD = "123456"
# python變量建議都用小寫，用下劃線分隔單詞，不用駝峰命名
print("please input account")
user_account = input()

print("please input password")
user_password = input()

if ACCOUNT == user_account and PASSWORD == user_password:
    print("success")
else:
    print("fail")

# encoding: utf-8
# snippet 片段

if condition:
    pass
else:
    pass


a = True
if a:
    # pass 空語句/占位語句
    pass
else:
    print("")


if True:
    pass
if False:
    pass

# 嵌套分支
if condition:
    if condition:
        pass
    else:
        pass
else:
    if condition:
        pass
    else:
        pass

# 代碼塊
if condition:
    code1
        code11
        code22
            code333
            code444
                code5555
                code6666
    code2
    code3
else:
    code1
    code2
    code3

改寫為elif

# encoding: utf-8
"""
a = x

a = 1 print("apple")
a = 2 print("orange")
a = 3 print("banana")

print("shopping")
"""

a = input()
print("a is" + a)
if a == 1:
    print("apple")
else:
    if a == 2:
        print("orange")
    else:
        if a == 3:
            print("banana")
        else:
            print("shopping")


# 改寫為elif
a = input()
print(type(a))
print("a is " + a)
a = int(a)
if a == 1:
    print("apple")
elif a == 2:
    print("orange")
elif a == 3:
    print("banana")
else:
    print("shopping")

# encoding: utf-8
# 循環

# 循環語句

# while     for
# CONDITION = True
# while CONDITION:
#     print("I am while")

counter = 1
# 遞歸常用while
while counter <= 10:
    counter += 1
    print(counter)
else:
    print("EOF")

# encoding: utf-8

# 主要是用來遍歷/循環 序列或者集合、字典
# a = ["apple", "orange", "banana", "grape"]
# for x in a:
#     print(x)

# a = [["apple", "orange", "banana", "grape"], (1, 2, 3)]
# for x in a:
#     for y in x:
#         # print(y, end="")
#         print(y)
# else:
#     print("fruit is gone")


# a = [1, 2, 3]

# for x in a:
#     if x == 2:
#         # break 遇到x==2的時候終止，打印出1
#         # break
#         # continue 遇到x==2的時候跳過，打印出1，3
#         continue
#     print(x)
# else:
#     print("EOF")


a = [["apple", "orange", "banana", "grape"], (1, 2, 3)]
for x in a:
    # if "banana" in x:
    #     break
    for y in x:
        if y == "orange":
            # 內部循環跳出后，外部循環還在執行
            break
        print(y)
else:
    print("fruit is gone")

# encoding: utf-8
# for (i=0; i<10; i++){}

# 以上的for循環用python實現
# for x in range(0, 10):
#     # range(0,10) 表示從0開始的10個數字，并不包含10
#     print(x)


# for x in range(0, 10, 2):
#     # range(0,10,2) 2表示步長
#     print(x, end=" | ")
#     # 打印結果：0 | 2 | 4 | 6 | 8 |


for x in range(10, 0, -2):
    print(x, end=" | ")
    # 打印結果：10 | 8 | 6 | 4 | 2 |

# encoding: utf-8

a = [1, 2, 3, 4, 5, 6, 7, 8]

# for i in range(0, len(a), 2):
#     print(a[i], end=" | ")
    # 1 | 3 | 5 | 7 | 

b = a[0:len(a):2]
print(b)
    # [1, 3, 5, 7]