摘要：表達(dá)式表達(dá)式是運(yùn)算符和操作數(shù)所構(gòu)成的序列運(yùn)算符優(yōu)先級(jí)同級(jí)的運(yùn)算符的優(yōu)先級(jí)還是有區(qū)別的比如邏輯運(yùn)算符里的的優(yōu)先級(jí)大于兩個(gè)括號(hào)同級(jí)，左結(jié)合出現(xiàn)賦值符號(hào)時(shí)，右結(jié)合優(yōu)先級(jí)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(zhí)行推薦的，大型工程適合用

表達(dá)式（Expression）是運(yùn)算符（operator）和操作數(shù)（operand）所構(gòu)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(jí)的運(yùn)算符的優(yōu)先級(jí)還是有區(qū)別的 比如邏輯運(yùn)算符里的and的優(yōu)先級(jí)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(gè)括號(hào)同級(jí)，左結(jié)合
4
>>> a = 1
>>> b = 2
>>> c = a + b    //出現(xiàn)賦值符號(hào)時(shí)，右結(jié)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(yōu)先級(jí)：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(zhí)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(huán)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(dá)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(huán)

# 循環(huán)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(huán) 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(shí)候終止，打印出1
#         # break
#         # continue 遇到x==2的時(shí)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(nèi)部循環(huán)跳出后，外部循環(huán)還在執(zhí)行
            break
        print(y)
else:
    print("fruit is gone")

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

# 以上的for循環(huán)用python實(shí)現(xiàn)
# for x in range(0, 10):
#     # range(0,10) 表示從0開始的10個(gè)數(shù)字，并不包含10
#     print(x)


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


for x in range(10, 0, -2):
    print(x, end=" | ")
    # 打印結(jié)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]