What are the commonly used functions in python?

Python commonly used functions:

1. print() function: print a string

2. raw_input() function: capture characters from the user keyboard

3. len() function: calculate character length

4. format(12.3654, '6.2f'/'0.3%') function: implement formatted output

5. type () function: query the type of object

6. int() function, float() function, str() function, etc.: type conversion function

7. id() function: get The memory address of the object

8. help() function: Python’s help function

9. s.islower() function: determine the lowercase character

10. s.sppace () function: determine whether it is a space

11. str.replace() function: replace the character

12. import() function: import the library

13. math. sin() function: sin() function

14. math.pow() function: calculate the power function

15. 3**4: 3 to the fourth power

16. pow(3,4) function: 3 raised to the fourth power

17. os.getcwd() function: get the current working directory

18. listdir() function: display Files in the current directory

19. socket.gethostbyname() function: Get the IP address of a host

20. urllib.urlopen(url).read(): Open network content and store it

21. open().write() function: write a file

22. webbrowser.open_new_tab() function: create a new tab and use the browser to open the specified web page

23. def function_name(parameters): Custom function

24. time.sleep() function: stop for a period of time

25. random.randint() function: generate random numbers

26. range() function: returns a list, printing from 1 to 100

27. file.read() function: reads the file and returns a string

28. file .readlines() function: read a file and return a list

29. file.readline() function: read a line of file and return a string

30. ords() and chr(ASCII) Function: Convert a string to ASCII or ASCIIS\ to a string

31. find(s[,start,end]) function: Find s

32 from a string. strip(), lstrip(), rstrip() function: remove spaces

33. split() function: what to use to separate strings

34. isalnum() function: determine whether it is Valid numbers or characters

35. isalpha() function: determine whether all characters are characters

36. isdigit() function: determine whether all are numbers

37. lower () function: change the data to lowercase

38. upper() function: change the data to uppercase

39. startswith(s) function: determine whether the string starts with s

40. endwith(s) function: determine whether the string ends with s

41. file.write() function: write function

42. file.writeline () function: write to file

43. s.append() function: insert data at the end of the data

44. s.insert(3,-1) function: at 3 Insert data before the position -1

45. list() function: convert the string into a list

46. index(value) function: find the position of the first value in the data

47. list.extend() function: extract each piece of data and add it to the list

48. count() function: count the number of occurrences of a certain element in the data

49. list.remove("s") function: delete the first occurrence of s in the data

50. del list[2] function: delete the second element of the data

51. pop() function: remove the data at the specified position of the data, with a return value

52. remove("ha") function: remove the "ha" element in the original data

53. reverse() function: reverse order of the list

54. isinstance() function: determine whether a certain data is of a certain type

55. abs() function: Get the absolute value of a number

56. del x[2] function: delete the element with index 2 in list x

57. file.sort() function: sort the book data

58. tuple() function: Create a tuple

59. find() function: The search returns the index

60. join() function: split Reverse operation

61. { }: Create a dictionary

62. dict() function: Create a dictionary

63. clear() function: Clear all items in the dictionary

64. copy() function: copying a dictionary will modify all dictionaries

65. d.copy() function: copying a dictionary will only modify the current dictionary

66. get() function: Query elements in the dictionary

67. items() function: Return all dictionaries into a list

68. iteritems() function: Function with items function Same

69. popitem() function: remove elements from the dictionary

70. update() function: update one dictionary item with another dictionary item

71. pass: do nothing

72.exec: execute a piece of code

73.eval: calculate Python expression

74.ord() function: return a single character The int value of the string

75.zip(sep1, sep2) function: Create a new sequence of English parallel iteration

76.def hello(): Custom function

77.import() function: Load extension library

Related recommendations: "Python Tutorial"

Several commonly used built-in functions commonly used in Python:

abs(x) is used to return the absolute value

divmod(x,y) The function passes two numbers and returns a tuple of the result of x/y (quotient , remainder)

pow(x,y) is used to find the y power of x

all(iterable) An iterable object is passed into the function. If all the numbers in the object True will be returned only if all bool values ​​are true, otherwise it will return False

any(iterable) passes an iterable object into the function. If the bool value of a number in the object is true, True will be returned. If all numbers are 0, False will be returned.

chr (x) Pass in an ascii code to the function, convert the ascii into the corresponding character

ord(x) Pass in a character into the function, convert the character into the corresponding ascii code

hex () Hexadecimal

oct() Octal

bin() Binary

enumerate(x,y) The x passed in the function is a list , y is the initial value of the iteration, such as the following example:

li = ['baby','honey']
for item in li:
  print item
for item in enumerate(li,12):
  print item
for item in enumerate(li,13):
  print item[0],item[1]

s.format() is a new method used to format characters. The example is as follows:

s = 'I am {0}{1}'
print s.format('liheng','!')

Output results:

 I am liheng!

Combined use of map() and lambda function map(lambda,list)

•reduce() function

reduce() function is also a high-level built-in Python function. The parameters received by the reduce() function are similar to map(), a function f and a list, but the behavior is different from map(). The function f passed in by reduce() must receive two parameters. reduce() evaluates each element of the list. The element calls function f repeatedly and returns the final result value.

For example, write a function f that receives x and y and returns the sum of x and y:

def f(x, y):
    return x + y

Call reduce(f, [1, 3, 5, 7, 9 ]), the reduce function will do the following calculations:

First calculate the first two elements: f(1, 3), the result is 4;

Then calculate the result and the third element : f(4, 5), the result is 9;

Then calculate the result and the 4th element: f(9, 7), the result is 16;

Then calculate the result and the 4th element Calculation of 5 elements: f(16, 9), the result is 25;

Since there are no more elements, the calculation ends and the result 25 is returned.

The above calculation is actually the sum of all elements of list. Although Python has a built-in summation function sum(), it is also very simple to use reduce() to sum.

reduce() can also receive a third optional parameter as the initial value for calculation. If the initial value is set to 100, the calculation:

reduce(f, [1, 3, 5, 7, 9], 100)

The result will become 125, because the first round of calculation is:

Calculate the initial value and the first element: f( 100, 1), the result is 101.

Code block using reduce() for continuous multiplication

def f(x,y):
return x * y
print reduce(f,[2,4,5,7,12])

•filter() function (filter function)

filter() function is Python Another useful built-in high-order function, the filter() function receives a function f and a list. The function of this function f is to judge each element and return True or False. filter() automatically filters out incorrect elements based on the judgment result. Elements that meet the criteria return a new list consisting of elements that meet the criteria.

For example, to delete even numbers and keep odd numbers from a list [1, 4, 6, 7, 9, 12, 17], first, write a function to determine odd numbers:

def is_odd(x):
  return x % 2 == 1

Then, use filter() to filter out even numbers:

filter(is_odd, [1, 4, 6, 7, 9, 12, 17])

Result:

[1, 7, 9, 17]

#利用过滤函数filter()进行删除None和空字符串
def is_not_empty(s):
return s and len(s.strip()) > 0
l = ['test','str',None,'','','END']
print filter(is_not_empty,l)
 
# 利用函数filter()过滤出1~100中平方根是整数的数
import math
l = []
for x in range(1,101):
l.append(x)
def is_int(x):
r = int(math.sqrt(x))
return r * r == x
print filter(is_int,l)

or

import math
def is_sqr(x):
  r = int(math.sqrt(x))
  return r*r==x
print filter(is_sqr, range(1, 101))

•Custom sorting function

Python The built-in sorted() function can sort the list:

>>>sorted([36, 5, 12, 9, 21])
[5, 9, 12, 21, 36]

But sorted() is also a higher-order function. It can receive a comparison function to implement custom sorting. The definition of the comparison function is, Pass in two elements x and y to be compared. If x should be ranked in front of y, return -1. If x should be ranked after y, return 1. If x and y are equal, return 0.

Therefore, if we want to implement reverse sorting, we only need to write a reversed_cmp function:

def reversed_cmp(x, y):
  if x > y:
    return -1
  if x < y:
    return 1
  return 0

In this way, calling sorted() and passing in reversed_cmp can achieve reverse sorting :

>>> sorted([36, 5, 12, 9, 21], reversed_cmp)
[36, 21, 12, 9, 5]

sorted() can also sort strings. Strings are compared according to ASCII size by default:

>>> sorted(['bob', 'about', 'Zoo', 'Credit'])
['Credit', 'Zoo', 'about', 'bob']

'Zoo' is ranked before 'about' because of 'Z' The ASCII code is smaller than 'a'.

When sorting strings, sometimes it is more customary to ignore case sorting. Please use the sorted() high-order function to implement an algorithm that ignores case sorting.

l = ['bob','about','Zoo','Credit']
def cmp_ignore_case(s1,s2):
　　u1 = s1.upper()
　　u2 = s2.upper()
if u1 < u2:
　　return -1
if u1 > u2:
　　return 1
return 0
print sorted(l,cmp_ignore_case)

zip() Introduction to the use of function

eval(str) The function can convert str into an expression for execution

__import__ and getattr() The use of

#以字符串的形式导入模块和函数
temp = 'sys'
model = __import__(temp)
foo = 'path'
function = getattr(model,foo)
print function

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