Python Learning Notes Day02

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variable

Container to store data for richer storage

Declare Variables

Variable name = Data

Variable Naming Specification

  • Cannot use Chinese, English is recommended

  • Variables can use numbers but cannot start

  • Variable names cannot use special symbols, but can be underlined_

  • Case sensitive

  • Variable names need to be meaningful

  • Cannot conflict with keyword

data type

There are countless types of Python

Six Types

Number Type===Number Type

Int Type===Integer

Integer is also an integer

Keyword: int or integer

Mode 1: Decimal declaration

0~9

Sample Code

intvar = 250

print(intvar)
print(type(intvar))

Run Results

250
<class 'int'>
Mode 2 binary declaration

0 1

Sample Code

intvar = 0B10001

print(intvar)
print(type(intvar))

Run Results

17 (result output is decimal)
<class 'int'>
Mode 3: Octal declaration

0~7

Sample Code

intvar = 0o147

print(intvar)
print(type(intvar))

Run Results

103
<class 'int'>
Mode 4 hexadecimal declaration

0~9 ABCEDEF

Sample Code

intvar = 0x14af

print(intvar)
print(type(intvar))

Run Results

5295
<class 'int'>

Float Type===Float Type

  • Floating point number is decimal

  • Keyword: float or real or double

Method 1: Declare with decimals

Sample Code

floatvar = 3.1415926

print(floatvar)
print(type(floatvar))

Run Results

3.1415926
<class 'float'>
Method 2: Scientific Counting

Sample Code

floatvar = 3.5e10

print(floatvar)
print(type(floatvar))

Run Results

35000000000.0
<class 'float'>

Bool Type===Boolean

There are only two values: True and False

Sample Code

boolvar = True

print(boolvar)
print(type(boolvar)

Run Results

True
<class 'bool'>

Complex Type===Complex Number

Method 1: Use an expression

Sample Code

comvar = 55 + 22j

print(comvar)
print(type(comvar))

Run Results

(55+22j)
<class 'complex'>
Method 2: Use specific functionality

Sample Code

comvar = complex(22, 55)

print(comvar)
print(type(comvar))

Run Results

(22+55j)
<class 'complex'>

String Type===String Type

The declaration of a string

Method 1: Single quotation mark declaration string''

Sample Code

strvar = '123'

print(strvar)
print(type(strvar))

Run Results

123
<class 'str'>

Method 2: Double quotation mark declaration string ""

Sample Code

strvar = "123"

print(strvar)
print(type(strvar))

Run Results

123
<class 'str'>

Method 3: Three quotes declare the string'''''or'''''

Sample Code

strvar = '''123'''

print(strvar)
print(type(strvar))

Run Results

123
<class 'str'>

Selection of String Declarations

  • If there are double quotes in the string, it is recommended to declare them in single quotes
  • Double quotation marks are recommended if there are single quotation marks in the string
  • Triple quotation marks are recommended if the string contains both double and single quotation marks.

Escape Characters: Changing the Meaning and Function of Characters

Sample Code

strvar = '1\'2\'3'

print(strvar)
print(type(strvar))

Run Results

1'2'3
<class 'str'>
Common escape characters
\n denotes a line break symbol
 \r means carriage return, not the return key, back to the beginning of the current line
 \'denotes a single quotation mark character (no function)
\"Represents a double quotation mark character (no function)
\Represents a backslash (no function)
\Continuation Character Good
 \t denotes indentation symbols

Sample Code

strvar = 'Abed, I see a silver light,\n Suspected frost on the ground'

print(strvar)


strvar = 'Look at the bright moon,\r Look down at your home'

print(strvar)


strvar = 'Look at the bright moon,\t Look down at your home'

print(strvar)


strvar = 'Look at the bright moon,\
//Look down at your home'

print(strvar)

Run Results

Abed, I see a silver light,
Suspected frost on the ground
 Look down at your home
 Looking up at the moon, looking down at home
 Raising my head, I see the moon so bright; withdrawing my eyes, my nostalgia comes around

Metacharacter: Output in a string-defined format without escaping any escape characters

Sample Code

strvar = r'Bedside\t bright\'Moonlight\',\n Doubtfully\'Frost\''

print(strvar)


strvar = R'Bedside\t bright\'Moonlight\',\n Doubtfully\'Frost\''

print(strvar)

Run Results

Bedside\tMing\moonlight\\n Suspected frost\
Bedside\tMing\moonlight\\n Suspected frost\

Enter key is not a return symbol

Under Windows platform:\r\n

On Linux platform:\n

Under Macos platform: \r Before 10.9n After 10.9

List Type===List Type

  • Ordered Containers

  • The value of a specific item can be modified

Declaration List

Sample Code

#             0       1       2          3    4
listvar = ['army officer's hat ornaments', 'Xishi', 'Yang Yuhuan ', 'Wang Zhaojun', 4]
#            -5      -4      -3         -2   -1
print(listvar)
print(type(listvar))

print(listvar[1])
print(type(listvar[1]))

listvar[2] = 'favorite concubine of emperor Minghuang'

print(listvar)
print(type(listvar))

Run Results

['Mink Cicada','Xishi','Yang Yuhuan','Wang Zhaojun', 4]
<class 'list'>
Xishi
<class 'str'>
['Mink Cicada','Xishi','Yang Guifei','Wang Zhaojun', 4]
<class 'list'>

Tuple Type===Tuple Type

  • Ordered Containers

  • The value of a specific item cannot be modified, and the modification will result in an error.

Tuple declaration

Specific code

#             0       1       2          3     4
tuplevar = ('army officer's hat ornaments', 'Xishi', 'Yang Yuhuan ', 'Wang Zhaojun', 4)
#            -5      -4      -3         -2    -1
print(tuplevar)
print(type(tuplevar))

print(tuplevar[1])
print(type(tuplevar[1]))

Run Results

('Mink Cicada','Xishi','Yang Yuhuan','Wang Zhaojun', 4)
<class 'tuple'>
Xishi
<class 'str'>

Set Type===Set Type

  • Unordered combination of a specific set of data

  • Data in a collection is not duplicated

  • Collection has no order

Collection declaration

Sample Code

setvar = {'army officer's hat ornaments', 'Xishi', 'Yang Yuhuan ', 'Wang Zhaojun', 4}

print(setvar)
print(type(setvar))

setvar = {'army officer's hat ornaments', 'Xishi', 'Xishi', 'Xishi', 'Yang Yuhuan ', 'Wang Zhaojun', 4}

print(setvar)
print(type(setvar))

Run Results

{4, 'Wang Zhaojun', 'Yang Yuhuan ', 'Xishi', 'army officer's hat ornaments'}
<class 'set'>
{4, 'Wang Zhaojun', 'Yang Yuhuan ', 'Xishi', 'army officer's hat ornaments'}
<class 'set'>

Dict Type===Dictionary Type

  • A set of data consisting of keys and values

  • Key: character or number

  • Value: Any data type

Sample Code

dictvar = {'Pedestrian': 'Wusong', 'Little Cyclone': 'Chaijin', 'Zhiduoxin': 'Wu Yong'}
#            Key Value
print(dictvar)
print(type(dictvar))

print(dictvar['Little Cyclone']) #Value can only be checked by key

Run Results

{'Pedestrian':'Wusong','Small Cyclone':'Chai Jin','Zhiduoxing':'Wu Yong'}
<class 'dict'>
Chaijin
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Tags: Python Windows Linux

Posted on Fri, 31 Jan 2020 21:58:53 -0500 by paradigmapc