Python common public methods

1 Python built-in functions

Python contains the following built-in functions:

function	description	Remark
Only (item)	Count the number of elements in the container
del(item)	Delete variables	There are two ways del
max(item)	Returns the maximum container element	If the dictionary, comparing only for key
min(item)	Returns the minimum container element	If the dictionary, comparing only for key
cmp(item1, item2)	Compare two values, less than -1 / 0 is equal to / greater than 1	Python 3.x cancel the function cmp

note

String more in line with the following rules: "0" < "A" < "a"

2 slices

description	Python expression	result	Supported data types
slice	"0123456789"[::-2]	"97531"	Strings, lists, tuples

Slice using the index value to limit the scope, from a larger string of cut small string
Lists and tuples are ordered set, it can be by an index value obtained corresponding data
Dictionary is an unordered collection that is using a key-value pairs stored data

Operator 3

Operators	Python expression	result	description	Supported data types
+	[1, 2] + [3, 4]	[1, 2, 3, 4]	merge	Strings, lists, tuples
*	["Hi!"] * 4	[ 'Hi', 'Hi', 'Hi', 'Hi!']	repeat	Strings, lists, tuples
in	3 in (1, 2, 3)	True	Element exists	Strings, lists, tuples, dictionaries
not in	4 not in (1, 2, 3)	True	Whether the element does not exist	Strings, lists, tuples, dictionaries
> >= == < <=	(1, 2, 3) < (2, 2, 3)	True	Compare elements	Strings, lists, tuples

note

inOut of the dictionary operation, it is determined that the dictionary key
inAnd not init is referred to as members of the operator

Member operator

Member operator for the test sequence contains a specified member

Operators	description	Examples
in	If you find the value in the specified sequence returns True, otherwise False	`3 in (1, 2, 3)` return `True`
not in	If the value is not found in the specified sequence returns True, otherwise False	`3 not in (1, 2, 3)` return `False`

Note: for the dictionary operation, it is determined that the dictionary key

4 complete syntax for loop

In Pythonthe complete for 循环syntax is as follows:

for variables in the set: 
    
    the loop body code for 
the else : 
    no pass break exits the loop, the loop is finished, the code will be executed

Scenarios

In iterate through data nested type, for example, a list contains a plurality of dictionaries
Requirements: To determine whether there is a specified value in a dictionary
- If there is , prompt and exit the loop
- If not present , the whole end of the cycle after, hoping to get a unified tips

students = [
    {"name": "阿土",
     "age": 20,
     "gender": True,
     "height": 1.7,
     "weight": 75.0},
    {"name": "小美",
     "age": 19,
     "gender": False,
     "height": 1.6 ,
      " weight " : 45.0 }, 
] 
find_name = " Ado " 
for stu_dict in Students.: 

    Print (stu_dict) 

    # determines current dictionary name traversed whether find_name 
    IF stu_dict.get ( ' name ' ) == find_name:
         Print ( " found " ) 

        # If you have found a direct exit the loop, do not need to follow-up data were compared 
        BREAK 

the else :
     Print ( " not found " ) 

Print (" Cycle end " )

Range

# Range () is a function that can be used to generate a sequence of natural numbers 
R & lt Range = (. 5) # generated such a sequence of [0,1,2,3,4] 
R & lt Range = (0, 10 ) 
R & lt Range = (10,0, -1 )
 # this function takes three parameters 
#    1 starting position (may be omitted, the default is 0) 
#    2. the end position of 
#    3 step (can be omitted, the default is 1) 

# Print (List (R & lt)) 

# by range () to create a perform the specified number of times for the cycle 
# for () loop in addition to the way to create the others are and while the same, 
#    including the else, including break continue can be circulated for use 
#    and also easier for recycling 
# will use a while loop before doing exercises, and then use a for loop to complete once! 
for I in Range (30 ):
     Print (I)

# for s in 'hello':
#     print(s)

The following highlights about the slice

Completion of a similar feeling java interception

# Slice 
# slicing refers to the existing list, get a list of a child 
# When you create a list, create a list of general, variable names will use the plural 
stus = [ ' Monkey King ' , ' Pig ' , ' sand monk ' , ' monk ' , ' spider ' , ' White Skeleton ' ] 

# index list may be negative 
# If the index is negative, after obtaining from the front element, -1 represents the inverse of the first, penultimate and so represents -2 
print (stus [-2 ]) 

# acquired by slicing a specified element 
# syntax: list [start: end] 
#    is acquired by slicing element, the element may include a starting position, the end position does not include the elements 
#   When do the slicing operation, always returns a new list, will not affect the original list of 
#    start and end positions of the indexes can be omitted 
#    If you omit end position, it will have been intercepted in the end 
#    If you omit the starting position , will start from the first element, taken 
#    If the start and end positions omitted entirely, is equivalent to a copy of a list of 
Print (stus [. 1 :])
 Print (stus [:. 3 ])
 Print (stus [ 1:. 4 ])
 Print (stus [1:. 5: 2 ])
 Print (stus) 

# syntax: list [start: end: step] 
# step, said elements each acquisition interval, the default value is 1 
# Print (stus [0: 5: 3]) 
# step can not be zero, but can be negative 
# Print (stus [:: 0]) ValueError: Slice the sTEP cAN not bE ZERO 
# If it is negative, it will post the list of the forward edge portion of elements having 
print(stus [:: -. 1 ]) 

# string sections can 
STR = ' Hello ' 
Print (STR)
 Print (STR [. 1:. 3])

E: \ PyWorkSpace \ Venv \ the Scripts \ python.exe E: / PyWorkSpace / Venv / bbb.py 
spider 
[ ' pig ' , ' sand monk ' , ' monk ' , ' spider ' , ' White Skeleton ' ] 
[ ' Monkey ' , ' pig ' , ' sand monk ' ] 
[ ' pig ' , ' sand monk ' , ' Tang ' ] 
[ 'Pig ', ' Monk ' ] 
[ ' Monkey ' , ' pig ' , ' sand monk ' , ' monk ' , ' spider ' , ' White Skeleton ' ] 
[ ' White Skeleton ' , ' spider ' , ' monk ' , ' sand monk ' , ' pig ' , ' Monkey '] 
Hello 
the

Process finished with exit code 0