摘要：什么是變量假設(shè)兩個(gè)做數(shù)學(xué)運(yùn)算先把乘以，然后加上，最后再加上列表變量名的命名規(guī)則變量名命名只能使用字母數(shù)字下劃線變量名的首字母不能是數(shù)字系統(tǒng)關(guān)鍵字，不能用在變量名中保留關(guān)鍵字不是系統(tǒng)保留關(guān)鍵字，但是不建議作為變量名，否則極易出錯(cuò)動(dòng)態(tài)語(yǔ)言的特性
什么是變量
假設(shè)兩個(gè)list做數(shù)學(xué)運(yùn)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(guī)則
變量名命名只能使用字母、數(shù)字、下劃線
>>> 1a = 2 //變量名的首字母不能是數(shù)字
SyntaxError: invalid syntax
>>> A2 = "1"
>>> _2 = "1"
>>> A*B="1"
SyntaxError: can"t assign to operator
系統(tǒng)關(guān)鍵字，不能用在變量名中 保留關(guān)鍵字
>>> and = 1
SyntaxError: invalid syntax
>>> if = 2
SyntaxError: invalid syntax
>>> import = 3
SyntaxError: invalid syntax
>>> type = 3 //type不是系統(tǒng)保留關(guān)鍵字，但是不建議作為變量名，否則極易出錯(cuò)
>>> 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(dòng)態(tài)語(yǔ)言的特性，聲明時(shí)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(gè)新的字符串，不再是原來(lái)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(nèi)的列表可變
(1, 2, 3, [1, 2, "4"])
運(yùn)算符
1.算數(shù)運(yùn)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(yùn)算符：=，+=，-=，*=，/=，%=，**=，//=
>>> c = 1
>>> c = c+1
>>> print(c)
2
>>> c+=1
>>> print(c)
3
>>> c-=1
>>> print(c)
2
>>> c++ //python中沒(méi)有自增和自減運(yùn)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(guān)系）運(yùn)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(shí)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(yùn)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(rèn)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(yùn)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(jù)key返回
True
6.身份運(yùn)算符：is，is not
對(duì)象的三個(gè)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(gè)變量的身份（內(nèi)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(wú)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(shù)
True
>>> isinstance(a,int)
False
>>> isinstance(a,(int,str,float))
True
>>> isinstance(a,(int,float))
False
7.位運(yùn)算符：（==把數(shù)字當(dāng)作二進(jìn)制數(shù)進(jìn)行運(yùn)算==）
&按位與
|按位或
^按位異或
~按位取反
<<左移動(dòng)
>>右移動(dòng)
按位與運(yùn)算，每一個(gè)二進(jìn)制數(shù)位進(jìn)行對(duì)比，兩個(gè)都為1，則得到1，只要有一個(gè)為0，就得到0
>>> a = 2
>>> b = 3
>>> a & b
2
| 變量 |
|
|
轉(zhuǎn)換為十進(jìn)制 |
|
| a |
1 |
0 |
2 |
| b |
1 |
1 |
3 |
| 按位與 |
1 |
0 |
2 |
按位或運(yùn)算，每一個(gè)二進(jìn)制數(shù)位進(jìn)行對(duì)比，只要有一個(gè)為1，就得到1，兩個(gè)都為0，則得到0
>>> a = 2
>>> b = 3
>>> a | b
3
| 變量 |
|
|
轉(zhuǎn)換為十進(jìn)制 |
|
| a |
1 |
0 |
2 |
| b |
1 |
1 |
3 |
| 按位或 |
1 |
1 |
3 |
