内置函数

1, abs() 取绝对值

#abs(x)
#Return the absolute value of a number.
# The argument may be an integer or a floating point number.
# If the argument is a complex number, its magnitude is returned.
a = -1
print("abs(-1):", abs(a))

#result:
#abs(-1): 1

2, all(),any()

#all(iterable), any(iterable)
#all():Return True if all elements of the iterable are true (or if the iterable is empty)
#any():Return True if any element of the iterable is true. If the iterable is empty, return False.
list_number = [1, 2, 3, 0]
print("all() of list_number is:", all(list_number))
print("any() of list_number is:",any(list_number))

#Result:
#all() of list_number is: False
#any() of list_number is: True

3, bin(),oct(),hex()

#bin(x), oct(x), hex(x)
#bin(): Convert an integer number to a binary string. The result is a valid Python expression.
#oct(x): Convert an integer number to an octal string. The result is a valid Python expression.
#hex(x): Convert an integer number to a lowercase hexadecimal string prefixed with “0x”, for example:
i = 10
print("bin() of 10:", bin(10), type(bin(10)))
print("oct() of 10:", oct(10), type(oct(10)))
print("hex() of 10:", hex(10), type(hex(10)))

#Result
#bin() of 10: 0b1010 <class 'str'>
#oct() of 10: 0o12 <class 'str'>
#hex() of 10: 0xa <class 'str'>

4, bytes(),str()

#bytes()，str()
#bytes():Return a new “bytes” object, which is an immutable sequence of integers in the range 0 <= x < 256
#class str(object=b'', encoding='utf-8', errors='strict') Return a str version of object. See str() for details.

b_hello_gbk = bytes("中文", encoding="gbk")    #gbk编码，一个中文使用两个字符表示
b_hello = bytes("中文", encoding="utf-8")  #utf-8编码，一个中文字符使用3个字节表示
print("gbk encoding:", b_hello_gbk,type(b_hello_gbk))
print("utf-8 encoding:", b_hello,type(b_hello))

str_hello = str(b_hello,encoding="utf-8")
print(str_hello, type(str_hello))

#gbk encoding: b'xd6xd0xcexc4' <class 'bytes'>
#utf-8 encoding: b'xe4xb8xadxe6x96x87' <class 'bytes'>
#中文 <class 'str'>

5, chr(),ord()

#chr(), ord()
#chr(): Return the string representing a character whose Unicode code point is the integer i. For example, chr(97)
#returns the string 'a', while chr(8364) returns the string '€'.
#ord(): Given a string representing one Unicode character, return an integer representing the Unicode code point of
# that character. For example, ord('a') returns the integer 97 and ord('€') (Euro sign) returns 8364.
c = chr(65)
print(c, type(c))
i = ord('A')
print(i, type(i))

#Result
#A <class 'str'>
#65 <class 'int'>

6, complie(),eval(),exec()

#compile(), eval(), exec()
#compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)
#Compile the source into a code or AST object. Code objects can be executed by exec() or eval(). source can either
#be a normal string, a byte string, or an AST object. Refer to the ast module documentation for information on how
#to work with AST objects.
str_code = "for i in range(0, 4): print(i)"
exec_code = compile(str_code, '', 'exec')
exec(exec_code)

str = "3*4+5"
print('eval of str:', eval(str))

#Result:
#1
#2
#3
#eval of str: 17

7, divmod()

#divmod(a, b)
#Take two (non complex) numbers as arguments and return a pair of numbers consisting of their quotient and remainder 
#when using integer division. 
page,left = divmod(97, 10)
print(page,left)

#Result
#9 7

8, filter(),map()

#filter(), map()
#filter(function, iterable)
#Construct an iterator from those elements of iterable for which function returns true.
def filter_condition(number): #过滤条件函数，返回值为true，false，为true的元素将被filter过滤到
    if number > 3:
        return True
    return False
list_number = [1, 2, 3, 4, 5]
ret_filter1 = filter(filter_condition, list_number)  #filter的第一个参数是函数名，不带参数
print("filter1:",list(ret_filter1))  #ret_filter是一个filter类的对象，需要用list转化成列表
#filter与lambda 配合
ret_filter2 = filter((lambda a: a > 3), list_number)
print("filter2:", list(ret_filter2))

#map(function, iterable, ...)
#Return an iterator that applies function to every item of iterable, yielding the results.
def mapping(number): #map()相当于映射，对列表里索引元素加100
    return number + 100
ret_map1 = map(mapping, list_number)
print("map1:", list(ret_map1))
ret_map2 = map(lambda a: a + 100, list_number) #lambda表达式非常简洁
print("map2:",list(ret_map2))

#Result：
#filter1: [4, 5]
#filter2: [4, 5]
#map1: [101, 102, 103, 104, 105]
#map2: [101, 102, 103, 104, 105]

9, range()

#range(stop) #输出从0开始不包含stop的元素
#range(start, stop[, step])#输出从start开始，不包含stop，步长step
for i in range(5):  #输出从0开始,不包含5
    print(i)

for i in range(0, 10, 2): #输出从0开始，不包含10，步长2
    print(i)