range function
It can generate a specified number sequence
Use case:
'''
range(start,stop,step)
Parameters:
start : The starting value, the default value is 0
stop : End value
step: Optional. The default step value is 1
Return value: iteratable object, numeric sequence
'''
#How the range function is used
# Write only one parameter, that is, from zero to 10, 9
res = range(11)
# When there are two parameters, the first parameter is the start value and the second parameter is the end value (before the end value)
res = range(5,10)
# Three parameters, parameter 1 is the start value, parameter 2 is the end value, and parameter 3 is the step value
res = range(1,10,3)
# Gets a flashback sequence of numbers
res = range(10,0,-1)
res = range(10,0,-2)
res = range(-10,-20,-1)
res = range(-20,-10)
res = range(-10,10)
print(list(res))
How to extract the sequence of numbers returned by the range() function:
# Method for obtaining the sequence of numbers returned by the range function
res = range(10)
1. Turn into list List data
print(list(res))
# 2. Traversal through the for loop
for i in res:
print(i)
# 3. Convert to iterator and call with the next function
res = iter(res)
print(next(res))
print(next(res))
zip() function
zip function can accept multiple iteratable objects, and then combine the ith element in each iteratable object to form a new iterator
Example:
'''
Parameters:*iterables，Any iteratable object
Return value: an iterator that returns a tuple
'''
var1 = '1234'
var2 = ['a','b','c']
var3 = ('A','B','C','D')
# Call the zip function to form a new tuple iterator
res = zip(var1,var2,var3)
# print(res,type(res))
for i in res:
print(i)
'''
('1', 'a', 'A')
('2', 'b', 'B')
('3', 'c', 'C')
('4', 'd', 'D')
'''
# zip() combined with the * operator can be used to disassemble a list:
x = [1, 2, 3]
y = [4, 5, 6]
zipped = zip(x, y)
print(list(zipped))
print(zip(x, y)) # Iterator object,
print(*zip(x, y))# Combined multiple tuple data
Other built-in functions
Built in functions related to data type conversion
- int() converts other types of data to integers
- Convert float() to float type
- bool() to Boolean
- Convert complex() to complex
- str() to string type
- List to list type
- Tuple to tuple type
- Convert dict to dictionary type
- Convert set to collection type
Variable correlation function
- id() gets the ID ID ID of the current data
- type() gets the type string of the current data
- print() print of data
- input() gets the input data
- isinstance() detects whether it is the specified data type
Mathematical correlation function
# Mathematical correlation function # Gets the absolute value of a number print(abs(-99.99)) # Summation starts from start, sums items in iterable from left to right, and returns the total value print(sum([1,2,3])) # Get maximum print(max([1,2,3])) print(max(99,12,45)) # Get minimum value print(min([2,1,6,-9])) print(min(6,7,1,0,-2)) # The power operation returns the y-power of x print(pow(2,3)) # rounding r = round(3.1415926) r = round(3.1415926,2) # How many decimal places are reserved r = round(4.5) # Odd advance and even retreat 1.5 = 2, 2.5 = 2, 3.5 = 4, 4.5 = 4 print(r)
Binary correlation function
# bin() converts the numeric type to binary print(bin(123)) # 0b1111011 # int() converts binary to integer print(int(0b1111011)) #1 23 # oct() to octal 01234567 print(oct(123)) # 0o173 # hex() to hex 0123456789abcdef print(hex(123)) # 0x7b
# Convert characters to ascii
r = ord('a')
print(r)
# Convert ascii to characters
r = chr(65)
print(r)
Higher order function
sorted(iterable,[reverse,key])
Take out the elements in the iteratable data one by one, put them into the key function for processing, sort them according to the return result in the function, and return a new list
'''
Function: sorting
Parameters:
iterable Iteratable data (container type data, range Data sequence, iterator)
reverse Optional. Whether to reverse. The default is False，No inversion, True reversal
key Optional, can be a custom function or a built-in function
Return value: the sorted result
'''
arr = [3,7,1,-9,20,10]
# By default, it is sorted from small to large
res = sorted(arr) # [-9, 1, 3, 7, 10, 20]
# You can sort from large to small
res = sorted(arr,reverse=True) # [20, 10, 7, 3, 1, -9]
# Use the abs function (find the absolute value) as the key keyword parameter of sorted
res = sorted(arr,key=abs)
print(res)
# Using custom functions
def func(num):
print(num,num % 2)
return num % 2
arr = [3,2,4,6,5,7,9]
# Use custom functions in the sorted function to process data
res = sorted(arr,key=func)
print(res)
# Optimized version
arr = [3,2,4,6,5,7,9]
res = sorted(arr,key=lambda x:x%2)
print(res)
map(func, *iterables)
Each element in the passed in iteratable data is put into the function for processing, and a new iterator is returned
'''
Parameters:
func Function custom function|Built in function
iterables: Iteratable data
Return value: iterator
'''
# (1) Convert a list of string numbers to an integer number list
# ['1','2','3','4'] # ==> [1,2,3,4]
# Common treatment methods
varlist = ['1','2','3','4'] # ==> [1,2,3,4]
newlist = []
for i in varlist:
newlist.append(int(i))
print(newlist)
# Use the map function for processing
varlist = ['1','2','3','4']
res = map(int,varlist) # <map object at 0x104ea8890>
print(list(res))
# (2) [1,2,3,4] ==> [1,4,9,16]
# Common method
varlist = [1,2,3,4]
newlist = []
for i in varlist:
res = i ** 2
newlist.append(res)
print(newlist)
# Use the map function to process this data
varlist = [1,2,3,4]
def myfunc(x):
return x ** 2
res = map(myfunc,varlist)
print(res,list(res))
# Optimized version
res = map(lambda x:x**2,varlist)
print(res,list(res))
# Practice Homework
# (3) ['a','b','c','d'] ==> [65,66,67,68]
reduce(func,iterable)
Each time, take out two elements from iterable and put them into func function for processing to get a calculation result. Then put the calculation result and the third element in iterable into func function to continue the operation. The obtained result and the subsequent fourth element are added into func function for processing, and so on until the last element participates in the operation
'''
Parameters:
func: Built in function or custom function
iterable: Iteratable data
Return value: the final operation result
Note: use reduce Function needs to be imported from functools import reduce
'''
from functools import reduce
# (1) [5,2,1,1] ==> 5211
# Common method
varlist = [5,2,1,1]
res = ''
for i in varlist:
res += str(i)
res = int(res)
print(res,type(res))
'''
5 2 1 1
5 * 10 + 2 == 52
52 * 10 + 1 == 521
521 * 10 + 1 == 5211
'''
# Complete with reduce
def myfunc(x,y):
return x*10+y
varlist = [5,2,1,1]
# Call function
res = reduce(myfunc,varlist)
print(res,type(res))
# (2) Put the string '456' = = > 456
# How to solve the above problem when the int method cannot be used for type conversion
# Defines a function that returns an integer number given a string number
def myfunc(s):
vardict = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}
return vardict[s]
# 1. First use the map function to convert the numeric string into an integer number
iter1 = map(myfunc,'456')
# 2. The values in the number list are processed twice using lambda
iter2 = reduce(lambda x,y:x*10+y,iter1)
print(iter2)
filter(func,iterable)
Filter the data and take each element in iterable to func function for processing. If the function returns True, the data will be retained, and if it returns False, the data will be discarded
'''
Parameters:
func Custom function
itereble: Iteratable data
Return value: an iterator composed of retained data
'''
# It is required to keep all even numbers and discard all odd numbers
varlist = [1,2,3,4,5,6,7,8,9]
# Common method implementation
newlist = []
for i in varlist:
if i % 2 == 0:
newlist.append(i)
print(newlist)
# Processing with filter
Define a function to judge whether the current function is even, and even returns True，Odd return False
def myfunc(n):
if n % 2 == 0:
return True
else:
return False
# Call the filter function for processing
it = filter(myfunc,varlist)
print(it,list(it))
# Optimized version
it = filter(lambda n:True if n % 2 == 0 else False,varlist)
print(it,list(it))