6.3. High-order functions, common built-in functions, and 6.3 Built-in high-order functions

6.3. High-order functions, common built-in functions, and 6.3 Built-in high-order functions
Higher-order functions:

• You can pass a function as a parameter to another function;
• Returns a function.

# The return value is the function sum = lambda x, y: x + ysub = lambda x, y: x-ycalc_dict = {"+": sum ,"-": sub} def calc (x): return calc_dict [x] print (calc ('-') (5, 6) print (calc ('+') (5, 6 )) # Function filter with function parameters (lambda x: x> 5, range (20 ))

Common built-in functions:

• Abs (x): returns the absolute value.
• Range ([start], stop [, step]): generates a sequence, starting from 0 by default.
• Note: The returned result is not a list object.

>>> Print (range (20) range (0, 20) >>> type (range (20 )) <class 'range' >>> isinstance (range (20), Iterable) ######### it is an iteratable object True >>>> from collections import Iterator >>>> isinstance (range (20), Iterator) # Not An iterator object, False

• Oct (x)
  Convert a number to an octal number.
• Hex (x)
  Convert integer x to a hexadecimal string
• Bin (x)
  Convert integer x to a binary string

>>> oct(8)'0o10'>>> hex(8)'0x8'>>> bin(8)'0b1000'

• Chr (I): returns the Unicode Character corresponding to the integer I.
• Ord (x): converts a character to a corresponding Unicode addressing.

>>> Ord ('中') 20013 >>> chr (20013) '中'

• Enumerate (sequence [, start = 0]): returns an enumerated object. The next () method of this object returns a tuple

for i, value in enumerate(['A', 'B', 'C']):    print(i, value)

• Iter (o [, sentinel]): generates an object iterator. The second parameter represents the delimiter.

From collections import Iterator # the object that can be called by the next () function and continuously return the next value is called the Iterator: Iterator. Print (isinstance ([], Iterator) print (isinstance (iter ([]), Iterator ))

• Sorted (iterable [, cmp [, key [, reverse]) sorts iterated objects.

>>> l=[8,7,6,5,4,3,2,1]>>> sorted(l)[1, 2, 3, 4, 5, 6, 7, 8]

• Cmp (x, y): returns a negative number if x <y; x = y, returns 0; x> y, returns a positive number.

• All (iterable)
  1. All elements in the iteratable object are true.
  2. In particular, if the iteratable object is null, True is returned.

>>> l=[]>>> all(l)True>>> l=[1,2,3,4,5]>>> all(l)True>>> l=[1,2,3,4,5,0]>>> all(l)False

• Any (iterable)
  1. The element in the iteratable object is true when it is true.
  2. In particular, if the iteratable object is null, False is returned.

>>> l=[]>>> any(l)False>>> l=[0,0,0,0]>>> any(l)False>>> l=[0,0,0,0,5]>>> any(l)True>>>

• Eval (expression [, globals [, locals]): calculates the value of expression.

>>> str1="3+4">>> eval(str1)7

• Exec (object [, globals [, locals]): executes the Python statement stored in a string or file.

>>> str1="print('hello world')">>> exec(str1)hello world

• Compile (source, filename, mode [, flags [, dont_inherit])

• Compile source as a code or AST object. Code objects can be evaluated using exec statements or eval.
  1. Parameter source: string or AST (Abstract Syntax Trees) object.
  2. filename: name of the code file. If the code is not read from the file, some identifiable values are passed.
  3. Parameter model: specifies the type of the compiled code. You can specify it as 'exec ', 'eval', and 'singles '.
  4. Parameters flag and dont_inherit

str1 = "print('hello world')"c2 = compile(str1,'','exec')   exec(c2)str2="3+4"c3=compile(str2,'','eval')a=eval(c3)print(a)

• Id (object): The function is used to obtain the memory address of an object.

>>> id(str1)1514678732384>>> str2=str1>>> id(str2)1514678732384

• Isinstance (object, classinfo): determines whether the object is a class instance.

>>> isinstance(1,int)True>>> isinstance(1.0,int)False

• Len (s): Return length (number of bytes returned in ascll format, number of characters returned in unicode/or number of elements)

>>> A = B 'abc' >>> len (a) 3 >>> B = "I love China" >>> len (B) 4 >>> c = [1, 2, 3, 4] >>> len (c) 4

• Repr (object): converts an object to a string format that can be read by the interpreter.

>>> c=[1,2,3,4]>>> repr(c)'[1, 2, 3, 4]'>>> d={1:2,2:3,3:4}>>> repr(d)'{1: 2, 2: 3, 3: 4}'

• Type (object): type of the object returned

>>> type(1)<class 'int'>>>> type("123")<class 'str'>>>> type((1,2,3))<class 'tuple'>