1. Mathematical operation function

• Introduction to built-in functions:

Built in functions, which are built-in functions after Python installation

All built-in function usage websites officially provided by Python:
https://docs.python.org/zh-cn/3/library/functions.html

• Common mathematical operation functions:

1.abs() - find the absolute value
Usage:

abs(numerical value)

Example:

print(abs(-25))
# The result is print 25
print(abs(35))
# The result is print 35
print(abs(-2.56))
# The result is 2.56

2.round() - approximate value of floating point number
Usage:

round(numerical value,numerical value)
# The following values mean to retain several decimal places and can be omitted

Example:

print(round(2.57))
# The result is print 3
print(round(2.57,1))
# The result is print 2.6

3.pow() - find the index
Usage:

pow(x,y,z)
# x. Both y and z represent values
# The return value of this function is the Y power of x, which is equivalent to x**y
# If z exists, take the remainder of the calculated value, which is equivalent to (x**y)%z

Example:

print(pow(2,4))
# The result is print 16
print(pow(2,4,3))
print((2**4)%3)
# The results are all printed 1

4.divmod() - find quotient and remainder
Usage:

divmod(x,y) 
# Returns a tuple containing quotient and remainder (x//y,x%y)

Example:

print(divmod(8,2))
# The result is print (4, 0)
print(divmod(8,3))
# The result is printed (2, 2)

5.max() - find the maximum value
Usage:

max(x,y...)

Example:

print(max(1,500,100))
# The result is print 500

min() - find the minimum value
Same as max()

6.sum() - sum
Usage:

sum(iterable,start)
# iterable represents iteratable objects (list, tuple, set, etc.), and start adds and sums the calculated values of iterable again

Example:

print(sum([1,2,3]))
# The result is print 6
print(sum([1,2,3],2))
# The result is print 8

7.eval() - execute expression
Usage:

eval(expression[, globals[, locals]])
# Expression -- expression
# globals -- variable scope and global namespace. If provided, it must be a dictionary object
# locals -- variable scope and local namespace. If provided, it can be any mapping object

Example:

print(eval('1+2'))
# The result is print 3
a=5
b=3
print(eval('a+b'))
# The result is print 8
print(eval('a+b',{'a':2,'b':3}))
# The result is print 5

2. Type conversion function

• Common type conversion function

1. (Num) numeric type conversion

• int() - convert to integer

Usage:

int(x,base=Hexadecimal number)
# x stands for string or number, and base is an omitted parameter

Example:

print(int(2.5))
# The result is print 2
print(int('a',base=16))
# The result is 10, because the decimal value of a in hexadecimal is 10
print(int('0101',base=2))
# The result is print 5, because the decimal value of 0101 in binary is 5

• float() - convert to floating point number

Usage:

float(x)
# x stands for string or integer

Example:

print(float(2))
# The result is print 2.0

• str() - convert to string

Usage:

str(object='')
# Object represents an object

Example:

print(type(str(1)))
# The result is print < class' STR '>

2.ASCII conversion

• ord() - character to number (ASCII code)

Usage:

ord('character')
# Returns the ACSII code value corresponding to the character

Example:

print(ord('a'))
# The result is print 97

• chr() - numeric to character (ASCII code)

Usage:

chr(number)
# Returns the character corresponding to the ASCII code value

Example:

print(chr(66))
# The result is print B

3.bool() - convert to Boolean
Usage:

bool(x)
# x is the object to convert

Example:

print(bool(0))
# The result is print False
print(bool(1))
# The result is print True

4. Binary conversion

• bin() - decimal to binary

Usage:

bin(x)
# x is an integer

Example:

print(bin(20))
# The result is 0b10100
a=20
print(bin(a))
# The result is 0b10100

• hex() - decimal to hexadecimal

Usage:

hex(x)
# x is a decimal integer

Example:

print(hex(15))
# The result is 0xf

• oct() - decimal to octal

Usage:

oct(x)
# x is an integer

Example:

print(oct(10))
# The result is printed 0o12

5. Type conversion

• list() - Convert tuples to lists

Usage:

list(Tuple)
# Tuple is the tuple to be converted to a list

Example:

print(list((1,2,3)))
# The result is printed [1, 2, 3]

• tuple() - Convert list to tuple

tuple(sequence)
# Sequence is the sequence to be converted

Example:

print(tuple([1,2,3]))
# The result is printed (1, 2, 3)
print(tuple({'a':1,"b":2}))
# The result is print ('a ',' B ')

• dict() - create dictionary

Usage:

dict(**kwarg)
dict(mapping, **kwarg)
dict(iterable, **kwarg)
# **kwargs -- Keyword
# mapping -- container for elements
# Iteratable -- iteratable object

Example:

print(dict(a=15,b='xiaoli',c=[99,97,100]))
# The result is print {'a': 15, 'B': Xiaoli ',' C ': [99, 97, 100]}

• bytes() - convert to byte array

Returns a new (byte array) bytes object, which is an immutable sequence containing integers in the range of 0 < = x < 256
Usage:

bytes([source[, encoding[, errors]]])
# If source is an integer, an initialization array with a length of source is returned;
# If source is a string, convert the string into a byte sequence according to the specified encoding;
# If source is an iteratable type, the element must be an integer in [0, 255];
# If source is an object consistent with the buffer interface, this object can also be used to initialize bytes
# If no parameters are entered, the default is to initialize the array to 0 elements

Example:

print(bytes('good',encoding='utf-8'))
# The result is b'\xe5\xa5\xbd'
print(bytes('good'.encode('utf-8')))
# The result is b'\xe5\xa5\xbd'
# Both printing results are consistent and can be used
print(bytes('good'.encode('gbk')))
# The result is print b'\xba\xc3'

3. Sequence operation function

• Sequence operation function

1. Judgment

• all() - correct judgment

Usage:

all(iterable)
# iterable stands for tuples or lists
# The function is used to judge whether all elements in a given iteratable parameter iterable are True. If so, it returns True; otherwise, it returns False
# All elements are True except 0, empty and False

Example:

print(all([1,2,3]))
# The result is print True
print(all((1,2,0,23)))
# The result is print False

• any() - wrong judgment

Usage:

any(iterable)
# iterable stands for tuples or lists
# The function is used to judge whether the given iteratable parameters iterable are all False, and returns False. If one of them is True,
# Returns True The opposite of the all() function

Example:

print(any((0,False,1)))
# The result is True

2. Sorting

• sorted() - the function sorts all iteratable objects

Usage:

sorted(iterable, *, key=None, reverse=False)
# iterable represents an iteratable object
# key represents the element mainly used for comparison. There is only one parameter. The parameters of the specific function are taken from the iteratable object,
# Specifies an element in the iteratable object to sort
# Reverse stands for collation, reverse = True descending, reverse = False ascending (default ascending)

Example:

print(sorted([12,231,31],key=int,reverse=True))
# The result is printed [231, 31, 12]

Difference between sort and sorted:
Sort is a method applied to the list. sorted can sort all iteratable objects,
The sort method of list returns the operation on the existing list, while the built-in function sorted method returns a new list instead of the operation on the original basis

• reverse() - used to reverse the elements in the list

Usage:

list.reverse()
# Note: this function has no parameters and no return value, but it will sort the list elements in reverse

Example:

a=[1,20,17]
a.reverse()
print(a)
# The result is printed [17, 20, 1]

• range() - create a list of integers

Usage:

range(start, stop[, step])
# Start stands for the start of counting. It starts from 0 by default
# stop stands for the end of counting
#Step stands for step size, which is 1 by default

Example:

for Test in range(0,5):
    print(Test,end=' ')
# The result is print 0 1 2 3 4 
# end = '' means no line breaks, separated by '

3. Packing

• zip() - package the elements in the object into tuples

Usage:

zip([iterable, ...])
# iterable represents one or more iterators
# Return tuple list

Example:

a=zip(['Age','Name'],[15,'xiaoli'])
print(a)
# The result is print < zip object at 0x000002272ab0f2c0 >
print(list(a))
# View packaged files
# The result is printed [('Age', 15), ('Name', 'xiaoli')]

4. Traversal

• enumerate() - combine a traversable data object into an index sequence

Usage:

enumerate(sequence, [start=0])
# Sequence represents a sequence or other object that supports iteration
# start represents the starting position of the subscript
# The function is used to combine a traversable data object into an index sequence,
# Lists data and data subscripts at the same time, which is generally used in the for loop

Example:

for Test in enumerate(['Name','Age']):
    print(Test,end=' ')
# The result is print (0, 'Name') (1, 'Age') 

4. Set operation function

• Set set

Set (set) is a data type in Python. It is an unordered and non repeated set of elements. If repetition occurs, it will be automatically overwritten
Example:

a={1,2,3,1}
print(a)
# The result is print {1, 2, 3}

• Set operation function

1. Add, empty

• add() - add element

Usage:

aggregate.add(element)
# Note: only one element can be added at a time

Example:

a={1,2,3}
a.add(4)
print(a)
# The result is print {1, 2, 3, 4}

• clear() - clear elements

Usage:

aggregate.clear()
# Empty all

Example:

a={1,2,3}
a.clear()
print(a)
# The result is print set()

2. Collection operation

• difference() - find the difference set

Usage:

a.difference(b)
# Both a and b represent sets, and the difference set is the element that exists in a and does not exist in b

Example:

a={1,21,15}
b={1,20,11}
print(a.difference(b))
# The result is printed {21, 15}

• intersection() - find intersection

Usage:

a.intersection(b)
# Both a and b represent sets. Find the intersection, that is, the elements that exist in a and b

Example:

a={12,13,14}
b={12,13,10}
print(a.intersection(b))
# The result is print {12, 13}

• union() - Union

Usage:

a.union(b)
# Both a and b represent sets, union sets, that is, elements existing in a and elements existing in b

Example:

a={5,6,7}
b={12,4,2}
print(a.union(b))
# The result is printed {2, 4, 5, 6, 7, 12}

3. Remove, update

• pop() - randomly remove an element

Usage:

aggregate.pop()
# Randomly remove an element and get that element without parameters

Example:

a={1,25,13}
print(a.pop())
# The result is print 25 (may be different)

• discard - removes the specified element

Usage:

a={12,13,14}
a.discard(13)
print(a)
# The result is printed {12, 14}

• update() - update the collection

Usage:

a={1,12,8}
b={2,9,5}
a.update(b)
print(a)
# The result is printed {1, 2, 5, 8, 9, 12}