Basic statement

Conditional statements

Python Provides if、elif、else To make logical judgments

The format is as follows ：

if Judge the condition 1:
Execute statement 1...
elif Judge the condition 2:
Execute statement 2...
elif Judge the condition 3:
Execute statement 3...
else:
Execute statement 4...

Loop statement ：

for loop

for A loop can traverse any sequence

str = 'Python'
for s in str:
print(s)

Output results ：

P
y
t
h
o
n

while loop

Examples are as follows ：

m=0
while m<=5:
print(m)
m=m+1
print(m+1)

Output results ：

0
1
2
3
4
5
7

break

Use in for Circulation and while Loop statement , End cycle .

Examples are as follows ：

str = 'Python'
for s in str:
if s == 'o':
break
print(s)

Output results ：

P
y
t
h

continue

be used for for loop while Loop statement , Terminate the loop , Into the next loop

Examples are as follows ：

str = 'Python'
for s in str:
if s == 'o':
continue
print(s)

Output results ：

P
y
t
h
n

pass sentence

pass It's an empty statement , Generally used for occupying , Make the program complete

Count

value type

species describe Guide character Binary system from 0 and 1 form 0b or 0B octal from 0 To 7 form 0o or 0O Decimal system By default nothing Hexadecimal from 0 To 9、a To f、A To F form , Case insensitive 0x or 0X

Basic operation

operation describe x + yx and y And x - yx and y Difference x * yx and y The product of the x / yx and y The business of x // yx Divide y, Divide and conquer x % yx Divide y, modulus -xx Take the opposite +xx unchanged abs(x)x The absolute value of int(x) take x Convert to integer float(x) take x Convert to floating point complex(x, y) A with a real part x Deficiency part of harmony y Complex number ,y The default is 0.divmod(x, y)(x // y, x % y)pow(x, y)x Of y The next power x ** yx Of y The next power

Mathematical functions

Introduce mathematical module math

import math

Examples are as follows ：

import math
math.sqrt(1024)

math Functions in modules

function describe abs(x) return x The absolute value of ceil(x) return x The ascending integer of , Such as ：math.ceil(1.1) return 2floor(x) return x The lower rounding of , Such as ：math.floor(1.1) return 1exp(x) return e Of x The next power log(x) Return to e Bottom x The logarithmic log10(x) Return to 10 Bottom x The logarithmic pow(x, y) return x Of y The next power sqrt(x) return x The square root of factorial(x) return x The factorial

Random function

random modular

random(x) function

Randomly generate one 0 To 1 A real number in a range

uniform(x,y) function

Randomly generate one x Real numbers in the range to

character string

Basic operation

visit

Examples are as follows ：

s = 'Python'
print(s[0]) # Access the first character 
s = 'Python'
print(s[1:3]) # visit yt
print(s[:3]) # visit Pyt
print(s[3:]) # visit hon

Output results ：

P
yt
Pyt
hon

Single character encoding

ord() Function returns the encoding of the character ,chr Function to convert the encoding to characters

Escape character

Escape character describe \ When used at the end of a line , Use as continuation character \b Backspace （Backspace）\000 empty \n Line break \v Vertical tabs \t Horizontal tabs \r enter

Operator

Operator describe + Connector * Repeat output [] Get the characters in the string by index [ : ] Get a part of the string in Whether the string contains the specified character not in Whether the string does not contain the specified character r/R String output as is

Examples are as follows ：

s1 = 'Hello'
s2 = 'Python'
print('s1 + s2 -->', s1 + s2)
print('s1 * 2 -->', s1 * 2)
print('s1[0] -->', s1[0])
print('s1[0:2] -->',s1[0:2])
print('"H" in s1 -->','H' in s1)
print('"H" not in s1 -->','H' not in s1)
print('\\r -->', R'\r')

Output results ：

s1 + s2 --> HelloPython
s1 * 2 --> HelloHello
s1[0] --> H
s1[0:2] --> He
"H" in s1 --> True
"H" not in s1 --> False
\r --> \r

format

Python Use % Formatted string

Place holder describe %s Formatted string %d Formatted integer %f Format floating point numbers

Examples are as follows ：

print('Hello %s' % 'Python')
print('{0} {1}'.format('Hello', 'Python'))

Output results ：

Hello Python
Hello Python

A string of format() Method to format , This way is to replace the placeholders in the string with the passed in parameters {0}、{1}…

Sequence

Basic use

Indexes

Sequential indexes support non negative and negative numbers , The index is nonnegative , from 0 Start , As shown below

The index is negative, counting from right to left , from -1 Start , As shown in the figure

Examples are as follows ：

str = 'Python'
print('str[0] str[-6] =', str[0], str[-6])
print('str[5] str[-1] =', str[5], str[-1])

Output results ：

str[0] str[-6] = P P
str[5] str[-1] = n n

section

Slicing can access a range of elements , The syntax is shown below ：

sname[start : end : step]

• sname： Represents the name of the sequence ;
• start： Start index position （ Including the location ）, The default is 0;
• end： Indicates the end index position of the slice （ Does not include the location ）, The default is the length of the sequence ;
• step： step .

Examples are as follows ：

str = 'Python'
print(str[:3])
print(str[3:])
print(str[:])

Output results ：

Pyt
hon
Python
Pto

Built in functions

function describe len() Calculate the length of the sequence max() Find the largest element in the sequence min() Find the smallest element in the sequence list() Convert sequence to list str() Convert sequence to string sum() Calculate the sum of the elements sorted() Sort the elements enumerate() Combine a sequence into an index sequence , Use it more often for In circulation

Lists and tuples

list

establish

All the elements in the list are placed in one [] in , Use... Between adjacent elements , Separate , for example ：

A=[111,0.5,'python']

visit

Access the values in the list by index , It can be used : Intercept the elements in the range , for example ：

A=[666,0.5,'python']
print(A[0],A[1],A[2])
print(A[:])
print(A[1::2])

Output results ：

666 0.5 python
[666, 0.5, 'python']
[0.5]

to update

You can modify the elements in the list directly , It can also be used. append() Add a new element to the list , for example ：

A=[666,0.5,'python']
A[0]=111 # modify 
print(A)
A.append(222) # increase 
print(A[:])
print(A[1::2])

Output results ：

[111, 0.5, 'python']
[111, 0.5, 'python', 222]
[0.5, 222]

Delete

Use del Delete the elements in the list , for example ：

A=[666,0.5,'python']
del A[1]
print(A)

Output results ：

[666, 'python']

Common functions

count()

Count the number of times an element appears in the list ( It can also be used to count the occurrence of an element in a string Number of times and the number of times an element appears in a tuple ) for example ：

A=['a','a','a']
B='dfsagad'
C=(1,1,2,3,3,1)
print(A.count("a"))
print(B.count("a"))
print(C.count(1))

Output results ：

3
2
3

index()

Find an element in the list ( character string , Tuples ) The place where they all appear ( Index ), for example ：

A=['a','b','c']
print(A.index('b'))

Output results ：

1

remove()

Remove the first occurrence of an element in the list , for example ：

A=['a','b','c','b']
A.remove('b')
print(A)

Output results ：

['a', 'c', 'b']

sort()

Sort the elements in the list , for example ：

A=['a','f','g','b','c','b']
B=[4,2,3,1,1]
A.sort()
B.sort()
print(A)
print(B)

Output results ：

['a', 'b', 'b', 'c', 'f', 'g']
[1, 1, 2, 3, 4]

copy()

Copy list , for example ：

A=['a','b',1,2]
B=A.copy()
print(B)

Output results ：

['a', 'b', 1, 2]

Tuples

establish

All elements in a tuple are placed in parentheses (), in , Two adjacent elements are represented by , separate

visit

Access to the same list

modify

Elements in tuples cannot be modified , We can only operate on it by reassigning it

Delete

Elements in tuples cannot be deleted , We can only delete the entire tuple

Common functions

len()

Compute tuple ( Length of string , The number of elements in the list ) The number of elements in , for example ：

A=['a','b',1,2]
B=A.copy()
print(B)
print(len(A))
C='hjkvvj'
print(len(C))
E=(1,2,'d')
print(len(E))

Output results ：

['a', 'b', 1, 2]
4
6
3

max() and min()

Return a tuple ( list , character string ) Maximum element in , minimum value , for example ：

A=['a','b','g','f']
B='12345'
C=('a','b','g','f')
print(min(A),max(B),min(C))

Output results ：

a 5 a

tuple()

Convert list to tuple , for example ：

C=['a','b','g','f']
A=tuple(C)
print(A)

Output results ：

('a', 'b', 'g', 'f')