Hello,大家好,我是程序汪小陈
今天,我将为大家展示python基础小例子,帮助大家加深记忆,列举52个例子,快来看看吧~
绝对值或复数的模
In [1]: abs(-6)
Out[1]: 6
接受一个迭代器,如果迭代器的所有元素
都为真,那么返回True
,否则返回False
In [2]: all([1,0,3,6])
Out[2]: False
In [3]: all([1,2,3])
Out[3]: True
接受一个迭代器,如果迭代器里至少有一个
元素为真,那么返回True
,否则返回False
In [4]: any([0,0,0,[]])
Out[4]: False
In [5]: any([0,0,1])
Out[5]: True
调用对象的__repr__() 方法,获得该方法的返回值,如下例子返回值为字符串
In [1]: class Student():
...: def __init__(self,id,name):
...: self.id = id
...: self.name = name
...: def __repr__(self):
...: return 'id = '+self.id +', name = '+self.name
...:
...:
In [2]: xiaoming = Student(id='001',name='xiaoming')
In [3]: print(xiaoming)
id = 001, name = xiaoming
In [4]: ascii(xiaoming)
Out[4]: 'id = 001, name = xiaoming'
将十进制
转换为二进制
In [1]: bin(10)
Out[1]: '0b1010'
将十进制
转换为八进制
In [1]: oct(9)
Out[1]: '0o11'
将十进制
转换为十六进制
In [1]: hex(15)
Out[1]: '0xf'
测试一个对象是True, 还是False.
In [1]: bool([0,0,0])
Out[1]: True
In [2]: bool([])
Out[2]: False
In [3]: bool([1,0,1])
Out[3]: True
将一个字符串
转换成字节
类型
In [1]: s = "apple"
In [2]: bytes(s,encoding='utf-8')
Out[2]: b'apple'
将字符类型
、数值类型
等转换为字符串
类型
In [1]: i = 100
In [2]: str(i)
Out[2]: '100'
判断对象是否可被调用,能被调用的对象就是一个callable
对象,比如函数 str
, int
等都是可被调用的,但是例子4 中xiaoming
实例是不可被调用的:
In [1]: callable(str)
Out[1]: True
In [2]: callable(int)
Out[2]: True
In [3]: xiaoming
Out[3]: id = 001, name = xiaoming
In [4]: callable(xiaoming)
Out[4]: False
如果想让xiaoming
能被调用 xiaoming(), 需要重写Student
类的__call__
方法:
In [1]: class Student():
...: def __init__(self,id,name):
...: self.id = id
...: self.name = name
...: def __repr__(self):
...: return 'id = '+self.id +', name = '+self.name
...: def __call__(self):
...: print('I can be called')
...: print(f'my name is {self.name}')
...:
...:
In [2]: t = Student('001','xiaoming')
In [3]: t()
I can be called
my name is xiaoming
查看十进制整数对应的ASCII字符
In [1]: chr(65)
Out[1]: 'A'
查看某个ASCII字符
对应的十进制数
In [1]: ord('A')
Out[1]: 65
classmethod
装饰器对应的函数不需要实例化,不需要 self
参数,但第一个参数需要是表示自身类的 cls 参数,可以来调用类的属性,类的方法,实例化对象等。
In [1]: class Student():
...: def __init__(self,id,name):
...: self.id = id
...: self.name = name
...: def __repr__(self):
...: return 'id = '+self.id +', name = '+self.name
...: @classmethod
...: def f(cls):
...: print(cls)
将字符串编译成python能识别或可执行的代码,也可以将文字读成字符串再编译。
In [1]: s = "print('helloworld')"
In [2]: r = compile(s,"", "exec")
In [3]: r
Out[3]: at 0x0000000005DE75D0, file "", line 1>
In [4]: exec(r)
helloworld
创建一个复数
In [1]: complex(1,2)
Out[1]: (1+2j)
删除对象的属性
In [1]: delattr(xiaoming,'id')
In [2]: hasattr(xiaoming,'id')
Out[2]: False
创建数据字典
In [1]: dict()
Out[1]: {}
In [2]: dict(a='a',b='b')
Out[2]: {'a': 'a', 'b': 'b'}
In [3]: dict(zip(['a','b'],[1,2]))
Out[3]: {'a': 1, 'b': 2}
In [4]: dict([('a',1),('b',2)])
Out[4]: {'a': 1, 'b': 2}
不带参数时返回当前范围
内的变量、方法和定义的类型列表;带参数时返回参数
的属性,方法列表。
In [96]: dir(xiaoming)
Out[96]:
['__class__',
'__delattr__',
'__dict__',
'__dir__',
'__doc__',
'__eq__',
'__format__',
'__ge__',
'__getattribute__',
'__gt__',
'__hash__',
'__init__',
'__init_subclass__',
'__le__',
'__lt__',
'__module__',
'__ne__',
'__new__',
'__reduce__',
'__reduce_ex__',
'__repr__',
'__setattr__',
'__sizeof__',
'__str__',
'__subclasshook__',
'__weakref__',
'name']
分别取商和余数
In [1]: divmod(10,3)
Out[1]: (3, 1)
返回一个可以枚举的对象,该对象的next()方法将返回一个元组。
In [1]: s = ["a","b","c"]
...: for i ,v in enumerate(s,1):
...: print(i,v)
...:
1 a
2 b
3 c
将字符串str 当成有效的表达式来求值并返回计算结果取出字符串中内容
In [1]: s = "1 + 3 +5"
...: eval(s)
...:
Out[1]: 9
In [1]: import sys
In [2]: a = {'a':1,'b':2.0}
In [3]: sys.getsizeof(a) # 占用240个字节
Out[3]: 240
在函数中设定过滤条件,迭代元素,保留返回值为True
的元素:
In [1]: fil = filter(lambda x: x>10,[1,11,2,45,7,6,13])
In [2]: list(fil)
Out[2]: [11, 45, 13]
将一个整数或数值型字符串转换为浮点数
In [1]: float(3)
Out[1]: 3.0
如果不能转化为浮点数,则会报ValueError
:
In [2]: float('a')
ValueError Traceback (most recent call last)
in ()
----> 1 float('a')
ValueError: could not convert string to float: 'a'
格式化输出字符串,format(value, format_spec)实质上是调用了value的__format__(format_spec)方法。
In [104]: print("i am {0},age{1}".format("tom",18))
i am tom,age18
3.1415926 | {:.2f} | 3.14 | 保留小数点后两位 |
---|---|---|---|
3.1415926 | {:+.2f} | +3.14 | 带符号保留小数点后两位 |
-1 | {:+.2f} | -1.00 | 带符号保留小数点后两位 |
2.71828 | {:.0f} | 3 | 不带小数 |
5 | {:0>2d} | 05 | 数字补零 (填充左边, 宽度为2) |
5 | {:x<4d} | 5xxx | 数字补x (填充右边, 宽度为4) |
10 | {:x<4d} | 10xx | 数字补x (填充右边, 宽度为4) |
1000000 | {:,} | 1,000,000 | 以逗号分隔的数字格式 |
0.25 | {:.2%} | 25.00% | 百分比格式 |
1000000000 | {:.2e} | 1.00e+09 | 指数记法 |
18 | {:>10d} | ' 18' | 右对齐 (默认, 宽度为10) |
18 | {:<10d} | '18 ' | 左对齐 (宽度为10) |
18 | {:^10d} | ' 18 ' | 中间对齐 (宽度为10) |
创建一个不可修改的集合。
In [1]: frozenset([1,1,3,2,3])
Out[1]: frozenset({1, 2, 3})
因为不可修改,所以没有像set
那样的add
和pop
方法
获取对象的属性
In [1]: class Student():
...: def __init__(self,id,name):
...: self.id = id
...: self.name = name
...: def __repr__(self):
...: return 'id = '+self.id +', name = '+self.name
In [2]: xiaoming = Student(id='001',name='xiaoming')
In [3]: getattr(xiaoming,'name') # 获取xiaoming这个实例的name属性值
Out[3]: 'xiaoming'
In [1]: class Student():
...: def __init__(self,id,name):
...: self.id = id
...: self.name = name
...: def __repr__(self):
...: return 'id = '+self.id +', name = '+self.name
In [2]: xiaoming = Student(id='001',name='xiaoming')
In [3]: hasattr(xiaoming,'name')
Out[3]: True
In [4]: hasattr(xiaoming,'address')
返回对象的哈希值,值得注意的是自定义的实例都是可哈希的,list
, dict
, set
等可变对象都是不可哈希的(unhashable)
In [1]: hash(xiaoming)
Out[1]: 6139638
In [2]: hash([1,2,3])
TypeError Traceback (most recent call last)
in ()
----> 1 hash([1,2,3])
TypeError: unhashable type: 'list'
返回对象的帮助文档
In [1]: help(xiaoming)
Help on Student in module __main__ object:
class Student(builtins.object)
| Methods defined here:
|
| __init__(self, id, name)
|
| __repr__(self)
|
| Data descriptors defined here:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)
返回对象的内存地址
In [1]: id(xiaoming)
Out[1]: 98234208
获取用户输入内容
In [1]: input()
aa
Out[1]: 'aa'
int(x, base =10) , x可能为字符串或数值,将x 转换为一个普通整数。如果参数是字符串,那么它可能包含符号和小数点。如果超出了普通整数的表示范围,一个长整数被返回。
In [1]: int('12',16)
Out[1]: 18
判断object是否为类classinfo的实例,是返回true
In [1]: class Student():
...: def __init__(self,id,name):
...: self.id = id
...: self.name = name
...: def __repr__(self):
...: return 'id = '+self.id +', name = '+self.name
In [2]: xiaoming = Student(id='001',name='xiaoming')
In [3]: isinstance(xiaoming,Student)
Out[3]: True
In [1]: class undergraduate(Student):
...: def studyClass(self):
...: pass
...: def attendActivity(self):
...: pass
In [2]: issubclass(undergraduate,Student)
Out[2]: True
In [3]: issubclass(object,Student)
Out[3]: False
In [4]: issubclass(Student,object)
Out[4]: True
如果class是classinfo元组中某个元素的子类,也会返回True
In [1]: issubclass(int,(int,float))
Out[1]: True
使用iter(obj, sentinel)
, 返回一个可迭代对象, sentinel可省略(一旦迭代到此元素,立即终止)
In [1]: lst = [1,3,5]
In [2]: for i in iter(lst):
...: print(i)
...:
1
3
5
In [1]: class TestIter(object):
...: def __init__(self):
...: self.l=[1,3,2,3,4,5]
...: self.i=iter(self.l)
...: def __call__(self): #定义了__call__方法的类的实例是可调用的
...: item = next(self.i)
...: print ("__call__ is called,fowhich would return",item)
...: return item
...: def __iter__(self): #支持迭代协议(即定义有__iter__()函数)
...: print ("__iter__ is called!!")
...: return iter(self.l)
In [2]: t = TestIter()
In [3]: t() # 因为实现了__call__,所以t实例能被调用
__call__ is called,which would return 1
Out[3]: 1
In [4]: for e in TestIter(): # 因为实现了__iter__方法,所以t能被迭代
...: print(e)
...:
__iter__ is called!!
1
3
2
3
4
5
object 是所有类的基类
In [1]: o = object()
In [2]: type(o)
Out[2]: object
返回文件对象
In [1]: fo = open('D:/a.txt',mode='r', encoding='utf-8')
In [2]: fo.read()
Out[2]: '\ufefflife is not so long,\nI use Python to play.'
mode取值表:
字符 | 意义 |
---|---|
'r' |
读取(默认) |
'w' |
写入,并先截断文件 |
'x' |
排它性创建,如果文件已存在则失败 |
'a' |
写入,如果文件存在则在末尾追加 |
'b' |
二进制模式 |
't' |
文本模式(默认) |
'+' |
打开用于更新(读取与写入) |
base为底的exp次幂,如果mod给出,取余
In [1]: pow(3, 2, 4)
Out[1]: 1
In [5]: lst = [1,3,5]
In [6]: print(lst)
[1, 3, 5]
In [7]: print(f'lst: {lst}')
lst: [1, 3, 5]
In [8]: print('lst:{}'.format(lst))
lst:[1, 3, 5]
In [9]: print('lst:',lst)
lst: [1, 3, 5]
返回 property 属性,典型的用法:
class C:
def __init__(self):
self._x = None
def getx(self):
return self._x
def setx(self, value):
self._x = value
def delx(self):
del self._x
# 使用property类创建 property 属性
x = property(getx, setx, delx, "I'm the 'x' property.")
使用python装饰器,实现与上完全一样的效果代码:
class C:
def __init__(self):
self._x = None
@property
def x(self):
return self._x
@x.setter
def x(self, value):
self._x = value
@x.deleter
def x(self):
del self._x
生成一个不可变序列:
In [1]: range(11)
Out[1]: range(0, 11)
In [2]: range(0,11,1)
Out[2]: range(0, 11)
In [1]: rev = reversed([1,4,2,3,1])
In [2]: for i in rev:
...: print(i)
...:
1
3
2
4
1
四舍五入,ndigits
代表小数点后保留几位:
In [11]: round(10.0222222, 3)
Out[11]: 10.022
In [12]: round(10.05,1)
Out[12]: 10.1
返回一个set对象,集合内不允许有重复元素:
In [159]: a = [1,4,2,3,1]
In [160]: set(a)
Out[160]: {1, 2, 3, 4}
class slice(start, stop[, step])
返回一个表示由 range(start, stop, step) 所指定索引集的 slice对象,它让代码可读性、可维护性变好。
In [1]: a = [1,4,2,3,1]
In [2]: my_slice_meaning = slice(0,5,2)
In [3]: a[my_slice_meaning]
Out[3]: [1, 2, 1]
排序:
In [1]: a = [1,4,2,3,1]
In [2]: sorted(a,reverse=True)
Out[2]: [4, 3, 2, 1, 1]
In [3]: a = [{'name':'xiaoming','age':18,'gender':'male'},{'name':'
...: xiaohong','age':20,'gender':'female'}]
In [4]: sorted(a,key=lambda x: x['age'],reverse=False)
Out[4]:
[{'name': 'xiaoming', 'age': 18, 'gender': 'male'},
{'name': 'xiaohong', 'age': 20, 'gender': 'female'}]
求和:
In [181]: a = [1,4,2,3,1]
In [182]: sum(a)
Out[182]: 11
In [185]: sum(a,10) #求和的初始值为10
Out[185]: 21
tuple()
将对象转为一个不可变的序列类型
In [16]: i_am_list = [1,3,5]
In [17]: i_am_tuple = tuple(i_am_list)
In [18]: i_am_tuple
Out[18]: (1, 3, 5)
class type
(name, bases, dict)
传入一个参数时,返回 object 的类型:
In [1]: class Student():
...: def __init__(self,id,name):
...: self.id = id
...: self.name = name
...: def __repr__(self):
...: return 'id = '+self.id +', name = '+self.name
...:
...:
In [2]: xiaoming = Student(id='001',name='xiaoming')
In [3]: type(xiaoming)
Out[3]: __main__.Student
In [4]: type(tuple())
Out[4]: tuple
创建一个聚合了来自每个可迭代对象中的元素的迭代器:
In [1]: x = [3,2,1]
In [2]: y = [4,5,6]
In [3]: list(zip(y,x))
Out[3]: [(4, 3), (5, 2), (6, 1)]
In [4]: a = range(5)
In [5]: b = list('abcde')
In [6]: b
Out[6]: ['a', 'b', 'c', 'd', 'e']
In [7]: [str(y) + str(x) for x,y in zip(a,b)]
Out[7]: ['a0', 'b1', 'c2', 'd3', 'e4']