摘要：什么是變量假設兩個做數學運算先把乘以，然后加上，最后再加上列表變量名的命名規則變量名命名只能使用字母數字下劃線變量名的首字母不能是數字系統關鍵字，不能用在變量名中保留關鍵字不是系統保留關鍵字，但是不建議作為變量名，否則極易出錯動態語言的特性
什么是變量
假設兩個list做數學運算
>>> [1,2,3,4,5,6] [1,2,3]
Traceback (most recent call last):
File "", line 1, in
[1,2,3,4,5,6] [1,2,3]
TypeError: list indices must be integers or slices, not tuple
//A B,先把A乘以3，然后加上B，最后再加上列表A
>>> [1,2,3,4,5,6]*3+[1,2,3]+[1,2,3,4,5,6]
[1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 1, 2, 3, 4, 5, 6]
>>> A = [1,2,3,4,5,6]
>>> print(A)
[1, 2, 3, 4, 5, 6]
>>> B = [1,2,3]
>>> A*3 + B + A
[1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 1, 2, 3, 4, 5, 6]
變量名的命名規則
變量名命名只能使用字母、數字、下劃線
>>> 1a = 2 //變量名的首字母不能是數字
SyntaxError: invalid syntax
>>> A2 = "1"
>>> _2 = "1"
>>> A*B="1"
SyntaxError: can"t assign to operator
系統關鍵字，不能用在變量名中 保留關鍵字
>>> and = 1
SyntaxError: invalid syntax
>>> if = 2
SyntaxError: invalid syntax
>>> import = 3
SyntaxError: invalid syntax
>>> type = 3 //type不是系統保留關鍵字，但是不建議作為變量名，否則極易出錯
>>> print(type)
3
>>> type = 1
>>> type(1)
Traceback (most recent call last):
File "", line 1, in
type(1)
TypeError: "int" object is not callable
>>> 1(1)
Traceback (most recent call last):
File "", line 1, in
1(1)
TypeError: "int" object is not callable
python動態語言的特性，聲明時不需要指明變量類型
>>> a = "1"
>>> a = 1
>>> a = (1,2,3)
>>> a = {1,2,3}
值類型與引用類型
int、str、tuple是值類型（不可變），list、set、dict是引用類型（可變）
1.int
>>> a = 1
>>> b = a
>>> a = 3
>>> print(b)
1
2.list
>>> a = [1,2,3,4,5]
>>> b = a
>>> a[0] = "1"
>>> print(a)
["1", 2, 3, 4, 5]
>>> print(b)
["1", 2, 3, 4, 5]
>>> a = [1,2,3]
>>> id(a)
4405825224
>>> hex(id(a))
"0x1069b8ec8"
>>> a[0]="1"
>>> id(a)
4405825224
>>>
3.str
>>> a = "hello"
>>> a = a + "python" //a加上一個新的字符串，不再是原來的字符串了
>>> print(a)
hellopython
>>> b = "hello"
>>> id(b)
4405534032
>>> b = b + "python" //加上新的字符串后，id改變
>>> id(b)
4355329456
>>> "python"[0]
"p"
>>> "python"[0]="o"
Traceback (most recent call last):
File "", line 1, in
"python"[0]="o"
TypeError: "str" object does not support item assignment
4.tuple
>>> a = (1,2,3)
>>> a[0] = "1"
Traceback (most recent call last):
File "", line 1, in
a[0] = "1"
TypeError: "tuple" object does not support item assignment
>>> b = [1,2,3]
>>> b.append(4)
>>> print(b)
[1, 2, 3, 4]
>>> c = (1,2,3)
>>> c.append(4)
Traceback (most recent call last):
File "", line 1, in
c.append(4)
AttributeError: "tuple" object has no attribute "append"
>>> a = (1,2,3,[1,2,4])
>>> a[2]
3
>>> a[3]
[1, 2, 4]
>>> a[3][2]
4
>>> a = (1,2,3,[1,2,["a","b","c"]])
>>> a[3][2][1]
"b"
>>> a = (1,2,3,[1,2,4])
>>> a[2] = "3"
Traceback (most recent call last):
File "", line 1, in
a[2] = "3"
TypeError: "tuple" object does not support item assignment
>>> a[3][2] = "4"
>>> print(a) //元組內的列表可變
(1, 2, 3, [1, 2, "4"])
運算符
1.算數運算符：+，-，* ，/，//，%，**
>>> "hello"+"world"
"helloworld"
>>> [1,2,3]*3
[1, 2, 3, 1, 2, 3, 1, 2, 3]
>>> 3-1
2
>>> 3/2
1.5
>>> 3//2 //整除
1
>>> 5%2 //求余
1
>>> 2**2 //求N次方
4
>>> 2**5
32
2.賦值運算符：=，+=，-=，*=，/=，%=，**=，//=
>>> c = 1
>>> c = c+1
>>> print(c)
2
>>> c+=1
>>> print(c)
3
>>> c-=1
>>> print(c)
2
>>> c++ //python中沒有自增和自減運算符
SyntaxError: invalid syntax
>>> c--
SyntaxError: invalid syntax
>>> b=2
>>> a=3
>>> b+=a
>>> print(b)
5
>>> b-=a
>>> print(b)
2
>>> b*=a
>>> print(b)
6
3.比較（關系）運算符：==，！=，>，<，>=，<=
>>> 1==1
True
>>> 1>1
False
>>> 1>=1
True
>>> a>=b
Traceback (most recent call last):
File "", line 1, in
a>=b
NameError: name "a" is not defined
>>> a=1
>>> b=2
>>> a!=b
True
>>> b=1
>>> b+=b>=1 //b=b+True
>>> print(b)
2
>>> print(b>=1)
True
>>> 1>1
False
>>> 2>3
False
>>> "a">"b"
False
>>> ord("a")
97
>>> ord("b")
98
>>> "abc"<"abd" //實際上是a和a比，b和b比，c和d比
True
>>> ord("abc")
Traceback (most recent call last):
File "", line 1, in
ord("abc")
TypeError: ord() expected a character, but string of length 3 found
>>> ord("c")
99
>>> ord("d")
100
>>> [1,2,3]<[2,3,4]
True
>>> (1,2,3)<(1,3,2)
True
4.邏輯運算符：and，or，not
>>> True and True
True
>>> True and False
False
>>> True or False
True
>>> False or False
False
>>> not False
True
>>> not True
False
>>> not not True
True
0 被認為是False，非0 表示True
>>> 1 and 1
1
>>> "a" and "b"
"b"
>>> "a" or "b"
"a"
>>> not "a"
False
>>> a = True
>>> b = False
>>> a or b
True
>>> b and a
False
空字符串 False
>>> not 0.1
False
>>> not ""
True
>>> not "0"
False
空的列表 False
>>> not []
True
>>> not [1,2]
False
>>> [1] or []
[1]
>>> [] or [1]
[1]
>>> "a" and "b"
"b"
>>> "" and "b"
""
>>> 1 and 0
0
>>> 0 and 1
0
>>> 1 and 2
2
>>> 2 and 1
1
>>> 0 or 1
1
>>> 1 or 0
1
>>> 1 or 2
1
5.成員運算符：in，not in
>>> a = 1
>>> a in [1,2,3,4,5]
True
>>> b = 6
>>> b in [1,2,3,4,5]
False
>>> b not in [1,2,3,4,5]
True
>>> b = "h"
>>> b in "hello"
True
>>> b not in (1,2,3,4,5)
True
>>> b not in {1,2,3,4,5}
True
>>> b = "a"
>>> b in {"c":1}
False
>>> b = 1
>>> b in {"c":1}
False
>>> b = "c"
>>> b in {"c":1} //字典里面根據key返回
True
6.身份運算符：is，is not
對象的三個特征：id、value、type，判斷id用“is”，判斷value用“==”，判斷type用“isinstance”
>>> a = 1
>>> b = 1
>>> a is b
True
>>> a="hello"
>>> b="world"
>>> a is b
False
>>> c="hello"
>>> a is c
True
>>> a=1
>>> b=2
>>> a==b
False
>>> a=1
>>> b=1
>>> a is b
True
>>> a==b
True
>>> a=1
>>> b=1.0
>>> a==b
True
>>> a is b //is不是比較值相等，比較的是兩個變量的身份（內存地址）是否相等
False
>>> id(a)
4374928384
>>> id(b)
4376239272
>>> a={1,2,3}
>>> b={2,1,3}
>>> a==b //集合是無序的
True
>>> a is b
False
>>> id(a)
4433997384
>>> id(b)
4433996488
>>> c=(1,2,3)
>>> d=(2,1,3)
>>> c==d //元組是序列，是有序的
False
>>> c is d
False
>>> a=1
>>> b=2
>>> a==b
False
>>> a is b
False
>>> a = "hello"
>>> type(a) == int
False
>>> type(a) == str
True
>>> isinstance(a,str) //isinstance是判斷變量類型的函數
True
>>> isinstance(a,int)
False
>>> isinstance(a,(int,str,float))
True
>>> isinstance(a,(int,float))
False
7.位運算符：（==把數字當作二進制數進行運算==）
&按位與
|按位或
^按位異或
~按位取反
<<左移動
>>右移動
按位與運算，每一個二進制數位進行對比，兩個都為1，則得到1，只要有一個為0，就得到0
>>> a = 2
>>> b = 3
>>> a & b
2
| 變量 |
|
|
轉換為十進制 |
|
| a |
1 |
0 |
2 |
| b |
1 |
1 |
3 |
| 按位與 |
1 |
0 |
2 |
按位或運算，每一個二進制數位進行對比，只要有一個為1，就得到1，兩個都為0，則得到0
>>> a = 2
>>> b = 3
>>> a | b
3
| 變量 |
|
|
轉換為十進制 |
|
| a |
1 |
0 |
2 |
| b |
1 |
1 |
3 |
| 按位或 |
1 |
1 |
3 |
