Datawhale Python基础训练营作业（1）
变量、运算符与数据类型
注释
# 我是一个python的注释！我是绿色的！
""" 我是多行注释，我是红色的！ """
'\n我是多行注释，我是红色的！\n'
运算符
算术运算符
print(1+1) #加法
2
print(1*1)#乘法
1
print(1-1)#减法
0
print(3/2)#除法
1.5
print(3//2)#整除（地板除）
1
print(3%4)#取余
3
print(3**3) #幂
27
比较运算符
print(2>1)
True
print(2>= 4)
False
print(3 == 4) #3等于4嘛？
False
print(1<2) #1小于等于2嘛？
True
print(5 <= 2) #5小于等于2嘛？
False
print(3!=5) #3不等于5嘛？
True
逻辑运算符
print(3>2) and (3<5) # 3大于2且3小于5
True
print(1>3)or (9<2)
FalseFalse
print(not (2>1))
False
位运算符
这部分还需进一步学习二进制算法。
print(bin(4))
0b100
print(bin(5))
0b101
print(bin(~4))
-0b101
print(bin(4&5))
0b100
print(bin(4|5))
0b101
print(bin(4<<2))
0b10000
print(bin(4^5))
0b1
print(bin(4>>2))
0b1
三元运算法
#这是一个特别冗余的表达方式！
x, y = 4, 5
if x < y:small = x
else:small = yprint(small)
4
#用三元操作符可以做简化如下：x, y = 4, 5small = x if x < y else y
print(small)
4
letters = ['A','B','C']if 'A' in letters:print('A'+' exists')if 'H' not in letters:print('H' + ' not exists')
A exists
H not exists
比较两个变量均指向不可变的类型
a = 'hello'
b = 'hello'
print(a is b, a == b)
print(a is not b, a != b)
True True
False False
比较两个变量均指向可变类型, 这里需要注意以下a is b 和 a == b 运算的区别，is对比的是内存的地址， ==对比的是变量之间的值！
a = ['hello']
b = ['hello']
print(a is b, a == b)
print(a is not b, a != b)
False True
True False
运算符的优先级
- 规则1：一元运算符比其他运算符优先！
- 规则2：运算顺序为：算术运算>移位运算>位运算
- 逻辑运算是最后的！
print(-4 ** 2)
-16
print(3 ** -3)
0.037037037037037035
print(1<< 3 + 3 & 7)
0
print(-3 * 2 + 5 / -2 - 4)
-12.5
print(3 < 4 and 4 < 5)
True
变量和赋值
- 变量相当于一张白纸，要给他赋值！
- 变量名可以是数字、字母、下划线，不能以数字开头！
- 大小写敏感
teacher = 'a'teacher
'a'
first = 1
second = 2third = first + secondthird
3
myTeacher = "老马的程序人生"
yourTeacher = "小马的程序人生"
ourTeacher = myTeacher + ',' + yourTeacher
print(ourTeacher)
老马的程序人生,小马的程序人生
数据类型和变换
数据类型一共有三种，分别:
- int整型
- float浮点型
- bool布尔型。
a = 1110type(a)
int
Python都是对象，有属性和方法！
b = dir(int) #dir可用来查看属性和方法
b
['__abs__','__add__','__and__','__bool__','__ceil__','__class__','__delattr__','__dir__','__divmod__','__doc__','__eq__','__float__','__floor__','__floordiv__','__format__','__ge__','__getattribute__','__getnewargs__','__gt__','__hash__','__index__','__init__','__init_subclass__','__int__','__invert__','__le__','__lshift__','__lt__','__mod__','__mul__','__ne__','__neg__','__new__','__or__','__pos__','__pow__','__radd__','__rand__','__rdivmod__','__reduce__','__reduce_ex__','__repr__','__rfloordiv__','__rlshift__','__rmod__','__rmul__','__ror__','__round__','__rpow__','__rrshift__','__rshift__','__rsub__','__rtruediv__','__rxor__','__setattr__','__sizeof__','__str__','__sub__','__subclasshook__','__truediv__','__trunc__','__xor__','bit_length','conjugate','denominator','from_bytes','imag','numerator','real','to_bytes']
这个以后查文档的时候会用到
a = 1101
print(bin(a)) #换成二进制
print(a.bit_length()) #计算二进制长度！
0b10001001101
11
print(1, type(1))print(1., type(1.))a = 0.00000023
b = 2.3e-7
print(a)
print(b)
1 <class 'int'>
1.0 <class 'float'>
2.3e-07
2.3e-07
from decimal import Decimal
a = decimal.getcontext()
print(a)
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[InvalidOperation, DivisionByZero, Overflow])