1, Basic use

Input and output

• Use print()
• Use input()

notes:

• Single line comment, starting with #

• Multiline comment, using three pairs of single quotes or three pairs of double quotes

Coding specification:

• Don't put a semicolon at the end of the line
• Case sensitive
• It is suitable to add spaces and empty lines to make the code layout more elegant, beautiful and reasonable
• Use indentation to represent code blocks

2, Variables and data types

Variable:

• When defining a variable, you do not need to specify the type of the variable. You can assign a value to the variable directly
• Variable names should conform to naming conventions

Data types: integer, floating point, string, Boolean, null, etc

#!/usr/bin/env python3
# ­*­ coding: utf­8 ­*­
__author__ = 'early summer'
'''Data types: integer, floating point, string, Boolean, null, etc '''

# Integer int
a = 3454566666666666666
print(a)
print(type(a))

# Floating point float
b = 12.5
print(b, type(b))

# String str, which defines the string. Single quotation marks or double quotation marks can be used (single quotation marks are recommended)
c = 'ccc'
d = "ddd"
print(c, type(c))
print('Zhang San said:"Do you have chicken tonight?"')

# When a string has multiple lines, three pairs of single quotation marks can be used to represent multiple lines
e = ''' welcome to chuxia0811 '''
print(e)
print(type(e))

# Boolean bool, values: True, False
f = True
print(f, type(f))
g = 5 < 3
print(g)
print(5 + False)  # True means 1 and False means 0

# Null NoneType
h = None
print(h, type(h))

3, String

Type conversion

# Convert string to numeric value
a = '25'
b = int(a)
print(type(a), type(b))
c = '12.5'
d = float(c)
print(type(c), type(d))

# Converts a numeric value to a string
print('hello ' + str(25))  # Numeric types cannot be directly spliced with characters, and type conversion is required

String common methods

string = ' hello world '
print(string.islower())
print(string.isupper())
print(string.capitalize())
print(string.index('llo'))
print(string)
print(string.strip()) # Similar to trim in java
print(len(string))    # Call the len() function to get the length

Slice (very important)

name = 'tom cruise'
print(name[0])
print(name[4], name[len(name) - 1], name[-1])
print(name[1:5])  # Get characters with index [1,5]
print(name[:5])  # Represents a de novo acquisition
print(name[2:])  # Indicates getting to the end
print(name[1:8:2])  # For characters with index [1,8), take one from every two
print(name[::2])  # All characters, one for every two

format

# Format the string and specify a placeholder in the string

# Method 1: use% operator,% s represents any character,% d represents integer and% f represents floating point number
name = 'tomaaaa'
age = 20
height = 180.5
print('Hello, my name is' + name + '，Age:' + str(age) + '，Height:' + str(height))
print('Hello, my name is%2.4s，Age:%d，Height:%.2f' % (name, age, height))# 2.4s indicates that the string length is 2 ­ 4 digits,. 2f means two decimal places are reserved
print('Current time:%d year­%02d month­%d day' % (2018, 5, 14))# The specified month is two digits. If it is less than two digits, make up 0

# Method 2: use the format() method and use {} to represent the placeholder
print('Hello, my name is{0}，Age:{1}，Height:{2:.2f}'.format(name, age, height))
print('Hello, my name is{name}，Age:{age}，Height:{height}'.format(age=age, name=name, height=height))

# Method 3: add an f before the string and use {variable name} to embed the variable
print(f'Hello, my name is{name}，Age:{age}，Height:{height}')

4, Operator

Arithmetic operator, comparison operator, assignment operator, logical operator, bit operator, condition operator, member operator, identity operator

#!/usr/bin/env python3
# ­*­ coding: utf­8 ­*­
__author__ = 'early summer'
''' 
Python Operators supported in: 
1.Arithmetic operator 
    + ­ * / % // **Auto increment + + and auto decrement are not supported ­­ 
2.Comparison operator 
    > < >= <= == !=or<> 
3.Assignment Operators  
    = += ­= *= /+ %= **= 
4.Logical operator 
    and or not 
5.Conditional operator, also known as ternary operator 
    Syntax: the result when the condition is true if condition else Result when condition is false 
6.Bitwise Operators  
    And& or| wrong~ XOR^ Shift left<< Shift right>> 
7.member operator  
    innot in 
8.Identity operator 
    isis not '''

# 1. Arithmetic operator
print(3 + 5)
print(3 * 5)
print(30 * '­')# Multiplication can be used for strings
print(5 % 3)
print(5 // 3) # division, rounding
print(2 ** 3) # power
print(pow(2, 3))
i = 5
i = i + 1
print(i)


# 2. Comparison operator
j = 5
print(j > 2)
print(10 > j > 1) # This notation is not supported
print('abc' > 'acd') # Can be used for string comparison, comparing the Unicode encoding of strings

# 3. Assignment operator
a = 10
a += 5 # Equivalent to a= a+5
print(a)

# 4. Logical operators
print(True and False)
print(5 > 2 or 4 < 1)
print(not 5 > 2)
x = 0 # 0 means False, non-0 means True
y = 8
print(x and y)  # Returns y if x is True; otherwise, returns X
print(x or y)   # Returns x if x is True; otherwise, returns y
print(not x)    # Returns False if x is True, otherwise returns True

#5. Conditional operator, also known as ternary operator
print('aaa' if 5 < 2 else 'bbb')

# 6. Bitwise operator
a = 5 # 00000101
b = 8 # 00001000
print(a & b) # If both digits are 1, it will be 1, otherwise it will be 0
print(a | b) # As long as one bit is 1, it is 1, otherwise it is 0
print(~a) # 0 if 1, 1 if 0
print(a ^ b) # If the two digits are the same, it is 0 and the difference is 1
print(b >> 2) # All bits of binary are shifted 2 bits to the right

# 7. Member operator
c = [3, 5, 12, 15, 7, 2]
d = 5
print(d not in c)

# 8. Identity operator
m = [1, 3, 5, 7]
n = [1, 3, 5, 7]
x = n
print(m is n)
print(x is n)
''' 
is and == Differences between 
is Judge whether two variables refer to the same object 
== Judge whether the values of two variables are equal 
'''
print(m == n)

5, Lists and tuples

A list is an ordered collection that stores multiple values and can add or remove elements from the list

Tuple is similar to list in that it is also used to store multiple values, but the elements in tuple can only be initialized at the time of definition and cannot be modified after initialization

Summary: both list and tuple are built-in collections in Python, one variable and the other immutable

# ­­­ List list
# Define list, using []
names = ['tom', 'jack', 'alice', 'mike']
print(names)
print(type(names))

# Get / set element
print(names[1], names[:3])
names[0] = 'lucy'
print(names)

# Append element
names.append('zhangsan')

# Inserts an element at the specified location
names.insert(1, 'lisi')

# Delete element
names.remove('jack')

# Pop up element
print(names.pop(0))

# Get the number of elements
print(len(names))

# Different types of data can be stored
names.append(25) # Not recommended
names.append(True)
print(names)

# ­­­­­­ Tuple tuple
# Define tuples, using ()
nums = (3, 8, 13, 25, 38, 250)
print(nums)
print(type(nums))
int(nums[2], nums[-1])
print(nums[1:3])

# Destructuring assignment 
# a = nums[0]
# b = nums[1]
# c = nums[2]
# d = nums[3]
# e = nums[4]
# f = nums[5]
a, b, c, d, e, f = nums
print(a, b, c, d, e, f)

6, Conditional judgment

Judge according to the conditions to perform different operations
Use the if... elif... else statement

7, Circulation

Repetitive execution of an operation is called a loop

Two cycles:
while Loop
for... in loop

# ­­­­ for...in loop
ames = ['tom', 'jack', 'alice', 'mike']
for name in names:
    print(name, end=',')
print()

# Use the range() function to generate a sequence
for i in range(1, 100, 2): # Generate an integer sequence of [1100] in steps of 2
    print(i, end=',')
print()

# Calculate the sum of 1 to 100
sum = 0
for i in range(1, 101):
    sum += i
print(sum)

break and continue keyword

8, Dictionaries and collections

The full name of dict is dictionary. Use the key ­ value (key) ­ value) stores data, commonly referred to as map in other languages
set is unordered and cannot be repeated

# ­­­­ Dictionaries
# Define dict with curly braces {}, which is very similar to json in js
scores = {'tom': 98, 'jack': 100, 'alice': 60}
print(scores)
print(type(scores))

# obtain
print(scores['jack'])
print(scores.get('alice'))

# Add / set
scores['lucy'] = 89
scores['tom'] = 100

# Pop up (delete)
print(scores.pop('tom'))

# Determine whether the specified key exists
print('alice' in scores)
print(scores)

# ergodic
print(scores.keys())
print(scores.values())
print(scores.items())

for k in scores.keys():
    print(k, scores[k])
print('­' * 80)

for v in scores.values():
    print(v)
print('­' * 80)

for k, v in scores.items():
    print(k, v)
print('­' * 80)

# ­­­­­ Set set
# Define set with curly braces {}
# s = {3, 12, 5, 7, 34, 12, 3}
nums = [4, 23, 1, 23, 4, 23]
s = set(nums) # Call the set() function to convert the list to set and remove duplicate values
print(s)
print(type(s))

# add to
s.add(666) 
s.add(1)

# delete
s.remove(1)
print(s)

# ergodic
for i in s:
    print(i)