이 기사는 Python의 변수 및 연산자에 대한 코드 예제를 제공합니다. 특정 참조 값이 있으므로 도움이 될 수 있습니다.
변수란 무엇입니까
두 개의 목록이 수학 연산을 한다고 가정합니다
>>> [1,2,3,4,5,6] [1,2,3] Traceback (most recent call last): File "<pyshell#0>", line 1, in <module> [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]
변수 이름 명명 규칙
변수 이름에는 문자, 숫자, 밑줄만 사용할 수 있습니다.
>>> 1a = 2 //变量名的首字母不能是数字 SyntaxError: invalid syntax >>> A2 = '1' >>> _2 = '1' >>> A*B='1' SyntaxError: can't assign to operator
시스템 키워드는 변수에 사용할 수 없습니다. 이름에 예약어 있음
>>> and = 1 SyntaxError: invalid syntax >>> if = 2 SyntaxError: invalid syntax >>> import = 3 SyntaxError: invalid syntax >>> type = 3 //type不是系统保留关键字，但是不建议作为变量名，否则极易出错 >>> print(type) 3 >>> type = 1 >>> type(1) Traceback (most recent call last): File "<pyshell#1>", line 1, in <module> type(1) TypeError: 'int' object is not callable >>> 1(1) Traceback (most recent call last): File "<pyshell#2>", line 1, in <module> 1(1) TypeError: 'int' object is not callable
파이썬 동적 언어의 특징, 선언 시 변수 유형을 지정할 필요 없음
>>> a = '1'
>>> a = 1
>>> a = (1,2,3)
>>> a = {1,2,3}값 유형 및 참조 유형
int, str, tuple은 값 유형(불변), list, set, dict는 참조 유형(변수)입니다.
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加上一个新的字符串，不再是原来的字符串了 >>> print(a) hellopython >>> b = 'hello' >>> id(b) 4405534032 >>> b = b + 'python' //加上新的字符串后，id改变 >>> id(b) 4355329456 >>> 'python'[0] 'p' >>> 'python'[0]='o' Traceback (most recent call last): File "<pyshell#8>", line 1, in <module> '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 "<pyshell#21>", line 1, in <module> 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 "<pyshell#26>", line 1, in <module> 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 "<pyshell#7>", line 1, in <module> a[2] = '3' TypeError: 'tuple' object does not support item assignment >>> a[3][2] = '4' >>> print(a) //元组内的列表可变 (1, 2, 3, [1, 2, '4'])
Operators
1. /, //, %, **
>>> '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. 할당 연산자: =, +=, -=, *=, /=, %=, **=, //=
>>> c = 1 >>> c = c+1 >>> print(c) 2 >>> c+=1 >>> print(c) 3 >>> c-=1 >>> print(c) 2 >>> c++ //python中没有自增和自减运算符 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. 연산자: ==, ! =, >, <, >=, <=
>>> 1==1
True
>>> 1>1
False
>>> 1>=1
True
>>> a>=b
Traceback (most recent call last):
File "<pyshell#3>", line 1, in <module>
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' //实际上是a和a比，b和b比，c和d比
True
>>> ord('abc')
Traceback (most recent call last):
File "<pyshell#12>", line 1, in <module>
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)
True4. 논리 연산자: 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</p> <p>0은 False로 간주되며, 0이 아닌 경우 True</p> <pre class="brush:php;toolbar:false">>>> 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
빈 문자열 False
>>> not 0.1 False >>> not '' True >>> not '0' False
를 의미합니다. 빈 목록 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. 멤버쉽 연산자: 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} //字典里面根据key返回
True6. 항등 연산자: is, is not
객체의 세 가지 특성: id, value, type, "is"로 ID 판단, 사용 값을 판단하려면 "==", 유형을 판단하려면 "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不是比较值相等，比较的是两个变量的身份（内存地址）是否相等
False
>>> id(a)
4374928384
>>> id(b)
4376239272
>>> a={1,2,3}
>>> b={2,1,3}
>>> a==b //集合是无序的
True
>>> a is b
False
>>> id(a)
4433997384
>>> id(b)
4433996488
>>> c=(1,2,3)
>>> d=(2,1,3)
>>> c==d //元组是序列，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是判断变量类型的函数
True
>>> isinstance(a,int)
False
>>> isinstance(a,(int,str,float))
True
>>> isinstance(a,(int,float))
False7. 비트 연산자: (==숫자를 이진수로 연산==)
&bitwise AND
|비트 OR
^비트별 XOR
~비트별 부정
<<왼쪽으로 이동
>>오른쪽으로 이동
비트별 AND 연산, 각 이진수를 비교하여 둘 다 1이면 1을 얻고, 하나가 0이면 0
>>> a = 2 >>> b = 3 >>> a & b 2
| Variable | 10진수로 변환 |
|
||
|---|---|---|---|---|
| a | 을 얻습니다.1 | 0 | 2 | |
| b | 1 | 1 | 3 |
|
| 비트 AND | 1 | 0 | 2 십진수로 변환 b1 |
1 |
| 1 |
1 |
3 |
|---|
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