Python3高级基础

Posted 2020-11-02 既生喻何生亮(Bright)

本文主要讲解Python高级基础编程方法。

[TOC]

Introducing Python Object Types

对象类型的优势

1. Built-in objects make programs easy to write
2. Built-in objects are components of extensions
3. Built-in objects are often more efficient than custom data structures
4. Built-in objects are a standard part of the language

Python的核心数据类型

数字 = Number

123+222 #整数的加法

345

1.5 * 4 #浮点型的乘法

6.0

2**100 # 2的100次幂

1267650600228229401496703205376

len(str(2 ** 100))

31

3.1415*2

6.283

import math # 导入数学模块
print(\'$\\pi$的数值是：{}\'.format(math.pi))
print(\'85的开方是：{}\'.format(math.sqrt(85)))

$\\pi$的数值是：3.141592653589793
85的开方是：9.219544457292887

import random
random.random()

0.6182188298420788

字符串

• 序列操作

S = \'bright\'
print(\'S的长度是: {}\'.format(len(S)))
print(\'第1个元素: {}\'.format(S[0]))
print(\'第2个元素: {}\'.format(S[1]))
print(\'第3个元素: {}\'.format(S[2]))
print(\'第4个元素: {}\'.format(S[3]))
print(\'第5个元素: {}\'.format(S[4]))
print(\'第6个元素: {}\'.format(S[5]))
print(\'最后1个元素第一种求法: {}\'.format(S[-1]))
print(\'最后1个元素第二种求法: {}\'.format(S[len(S)-1]))
print(\'倒数第2个元素: {}\'.format(S[-2]))

S的长度是: 6
第1个元素: b
第2个元素: r
第3个元素: i
第4个元素: g
第5个元素: h
第6个元素: t
最后1个元素第一种求法: t
最后1个元素第二种求法: t
倒数第2个元素: h

# 切片操作
print(\'Slice of S from offsets 1 through 2 (not 3): {}\'.format(S[1:3]))
print(\'Everything past the first (1:len(S)): {}\'.format(S[1:]))
print(\'S itself hasn\\\'t changed: {}\'.format(S))
print(\'Everything but the last: {}\'.format(S[0:6]))
print(\'Everything but the last again, but simpler (0:-1): {}\'.format(S[:-1]))
print(\'Same as S[0:6]: {}\'.format(S[:6]))
print(\'All of S as a top-level copy (0:len(S)): {}\'.format(S[:]))

Slice of S from offsets 1 through 2 (not 3): ri
Everything past the first (1:len(S)): right
S itself hasn\'t changed: bright
Everything but the last: bright
Everything but the last again, but simpler (0:-1): brigh
Same as S[0:6]: bright
All of S as a top-level copy (0:len(S)): bright

# 字符串的加法与乘法
S1 = \'I\'
S2 = \' like\'
S3 = \' you! \'
print(\'字符串的加法运算: {}\'.format(S1+S2+S3))
print(\'字符串的乘法运算: {}\'.format((S1+S2+S3)*3))

字符串的加法运算: I like you! 
字符串的乘法运算: I like you! I like you! I like you! 

• 字符串的不可变形 = immutability

Str1 = \'Yuxl\'
print(Str1)
try:
    Str1[0] = \'XX\'
except:
    print("不可更改")

Yuxl
不可更改

• We can run expressions to make new objects

print(\'Str1原来的形式: {}\'.format(Str1))
Str1 = \'XX\' + Str1[1:]
print(\'Str1修改后的形式: {}\'.format(Str1))

Str1原来的形式: Yuxl
Str1修改后的形式: XXuxl

• 字符串的类型方法

S = \'Spam\'
# S.find()
print(\'Find the offset of a substring: {}\'.format(S.find(\'pa\')))
# S.replace(S中有的字符，定义字符替换原字符)
print(\'Replace occurrences of a substring with another: {}\'.format(S.replace(\'pa\',\'XYZ\')))
print(\'替换后原字符串不变: {}\'.format(S))

Find the offset of a substring: 1
Replace occurrences of a substring with another: SXYZm
替换后源字符串不变: Spam

line = \'aaa,bbb,ccccc,dd\'
print(\'Split on a delimiter into a list of substrings: {}\'.format(line.split(\',\')))
line1 = \'aaa,bbb,ccccc,dd\\n\'
print(\'打印原line1: {}\'.format(line1))
print(\'Remove whitespace characters on the right side: {}\'.format(line.rstrip()))
print(\'打印操作后的line1: {}\'.format(line1))
print(\'-----------------------\')

Split on a delimiter into a list of substrings: [\'aaa\', \'bbb\', \'ccccc\', \'dd\']
打印原line1: aaa,bbb,ccccc,dd

Remove whitespace characters on the right side: aaa,bbb,ccccc,dd
打印操作后的line1: aaa,bbb,ccccc,dd

-----------------------

S = \'Bright\'
print(\'Upper- and lowercase conversions: {}\'.format(S.upper()))
print(\'Content tests: isalpha, isdigit, etc.: {}\'.format(S.isalpha()))

Upper- and lowercase conversions: BRIGHT
Content tests: isalpha, isdigit, etc.: True

S = \'A\\nB\\tC\' # \\n is end-of-line, \\t is tab
print(S)

A
B	C

len(S) #Each stands for just one character

5

print(\'\\\\n is a byte with the binary value 10 in ASCII: {}\'.format(ord(\'\\n\')))

\\n is a byte with the binary value 10 in ASCII: 10

S = \'A\\oB\\oC\'
print(S)
len(S)

A\\oB\\oC





7

msg = """ aaaaaaaaaaaaa
bbb\'\'\'bbbbbbbbbb""bbbbbbb\'bbbb
cccccccccccccc"""
print(msg)

 aaaaaaaaaaaaa
bbb\'\'\'bbbbbbbbbb""bbbbbbb\'bbbb
cccccccccccccc

msg

\' aaaaaaaaaaaaa\\nbbb\\\'\\\'\\\'bbbbbbbbbb""bbbbbbb\\\'bbbb\\ncccccccccccccc\'

• 模式匹配 = Pattern Matching

import re
match = re.match(\'Hello[ \\t]*(.*)world\', \'Hello    Python world\')
match.group(1)

\'Python \'

match = re.match(\'/(.*)/(.*)/(.*)\', \'/usr/home/lumberjack\')
match.groups()

(\'usr\', \'home\', \'lumberjack\')

列表 = lists

• 序列操作

L = [123,\'spam\',1.23]
print(\'Number of items in the list: {}\'.format(len(L)))
print(\'Indexing by position: {}\'.format(L[0]))
print(\'Slicing a list returns a new list: {}\'.format(L[:-1]))
print(\'Concatenation makes a new list too: {}\'.format(L+[4,5,6]))
print(\'We\\\'re not changing the original list: {}\'.format(L))

Number of items in the list: 3
Indexing by position: 123
Slicing a list returns a new list: [123, \'spam\']
Concatenation makes a new list too: [123, \'spam\', 1.23, 4, 5, 6]
We\'re not changing the original list: [123, \'spam\', 1.23]

• 类型方法操作

L = [123,\'spam\',1.23]
print(\'Growing: add object at end of list: {}, 列表{}\'.format(L.append(\'NI\'),L))
print(\'Shrinking: delete an item in the middle: {}\'.format(L.pop(2)))
print(\'"del L[2]" deletes from a list too: {}\'.format(L))
M = [\'bb\',\'aa\',\'cc\']
print(\'M排序: {},{}\'.format(M.sort(),M))
print(\'M元素翻转: {},{}\'.format(M.reverse(),M))

Growing: add object at end of list: None, 列表[123, \'spam\', 1.23, \'NI\']
Shrinking: delete an item in the middle: 1.23
"del L[2]" deletes from a list too: [123, \'spam\', \'NI\']
M排序: None,[\'aa\', \'bb\', \'cc\']
M元素翻转: None,[\'cc\', \'bb\', \'aa\']

• 列表嵌套 = nesting

M = [[1,2,3],
    [4,5,6],
    [7,8,9]]
print(M)
print(\'第2行: {}\'.format(M[1]))
print(\'Get row 2, then get item 3 within the row: {}\'.format(M[1][2]))
# 列表解析
col2 = [row[1] for row in M]
print(\'Collect the items in column 2: {}\'.format(col2))
print(\'The matrix is unchanged: {}\'.format(M))
print(\'Add 1 to each item in column 2: {}\'.format([row[1]+1 for row in M]))
print(\'Filter out odd items: {}\'.format([row[1] for row in M if row[1]%2==0]))
print(\'打印矩阵M: {}\'.format(M))
diag = [M[i][i] for i in [0,1,2]]
print(\'Collect a diagonal from matrix: {}\'.format(diag))
print(\'Repeat characters in a string: {}\'.format([c*2 for c in \'bright\']))

[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
第2行: [4, 5, 6]
Get row 2, then get item 3 within the row: 6
Collect the items in column 2: [2, 5, 8]
The matrix is unchanged: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Add 1 to each item in column 2: [3, 6, 9]
Filter out odd items: [2, 8]
打印矩阵M: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Collect a diagonal from matrix: [1, 5, 9]
Repeat characters in a string: [\'bb\', \'rr\', \'ii\', \'gg\', \'hh\', \'tt\']

print(\'打印M: {}\'.format(M))
G = (sum(row) for row in M)
print(\'Create a generator of row sums: {}\'.format(next(G)))
print(\'Run the iteration protocol: {}\'.format(next(G)))

打印M: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Create a generator of row sums: 6
Run the iteration protocol: 15

print(\'Map sum over items in M: {}\'.format(list(map(sum,M))))
print(\'Create a set of row sums: {}\'.format({sum(row)for row in M}))
print(\'Creates key/value table of row sums: {}\'.format({i : sum(M[i]) for i in range(3)}))
print(\'List of character ordinals: {}\'.format([ord(x) for x in \'spaam\']))
print(\'Sets remove duplicates: {}\'.format({ord(x) for x in \'spaam\'}))
print(\'Dictionary keys are unique: {}\'.format({x:ord(x) for x in \'spaam\'}))

Map sum over items in M: [6, 15, 24]
Create a set of row sums: {24, 6, 15}
Creates key/value table of row sums: {0: 6, 1: 15, 2: 24}
List of character ordinals: [115, 112, 97, 97, 109]
Sets remove duplicates: {112, 97, 115, 109}
Dictionary keys are unique: {\'s\': 115, \'p\': 112, \'a\': 97, \'m\': 109}

字典 = dictionary

• 映射操作

D = {\'food\': \'Spam\', \'quantity\': 4, \'color\': \'pink\'}
print(\'Fetch value of key \\\'food\\\': {}\'.format(D[\'food\']))
print(\'Add 1 to \\\'quantity\\\' value: {},\\n打印：{}\'.format(D[\'quantity\'] + 1 , D))
D = {}
# Create keys by assignment
D[\'Name\']=\'bright\'
D[\'Job\']=\'student\'
D[\'Style\']=\'popular\'
print(\'打印D: {}\'.format(D))
print(\'打印D[\\\'name\\\']: {}\'.format(D[\'Name\']))

Fetch value of key \'food\': Spam
Add 1 to \'quantity\' value: 5,
打印：{\'food\': \'Spam\', \'quantity\': 4, \'color\': \'pink\'}
打印D: {\'Name\': \'bright\', \'Job\': \'student\', \'Style\': \'popular\'}
打印D[\'name\']: bright

• 字典嵌套

rec = {\'name\': {\'first\': \'Bob\', \'last\': \'Smith\'},
\'job\': [\'dev\', \'mgr\'],
\'age\': 40.5}
print(\'打印rec的名字: {}\'.format(rec[\'name\']))
print(\'Index the nested dictionary: {}\'.format(rec[\'name\'][\'last\']))
print(\'\\\'job\\\' is a nested list: {}\'.format(rec[\'job\']))
print(\'# Index the nested list: {}\'.format(rec[\'job\'][-1]))
print(\'Expand Bob\\\'s job description in-place: {}\\n打印： {}\'.
      format(rec[\'job\'].append(\'janitor\'),rec))

打印rec的名字: {\'first\': \'Bob\', \'last\': \'Smith\'}
Index the nested dictionary: Smith
\'job\' is a nested list: [\'dev\', \'mgr\']
# Index the nested list: mgr
Expand Bob\'s job description in-place: None
打印： {\'name\': {\'first\': \'Bob\', \'last\': \'Smith\'}, \'job\': [\'dev\', \'mgr\', \'janitor\'], \'age\': 40.5}

• 字典排序整理

D = {\'a\':1,\'b\':2,\'c\':3}
print(\'D: {}\'.format(D))
print(\'Unordered keys list: {}\'.format(list(D.keys())))
print(\'Sorted keys list: {}\'.format((list(D.keys())).sort()))
for key in D.keys():
    print(key, \'=>\', D[key])

D: {\'a\': 1, \'b\': 2, \'c\': 3}
Unordered keys list: [\'a\', \'b\', \'c\']
Sorted keys list: None
a => 1
b => 2
c => 3

print(D)
for key in sorted(D):
    print(key, \'=>\', D[key])

{\'a\': 1, \'b\': 2, \'c\': 3}
a => 1
b => 2
c => 3

for c in \'bright\':
    print(c.upper())

B
R
I
G
H
T

x = 4
while x>0:
    print(\'bright!\'*x)
    x -= 1

bright!bright!bright!bright!
bright!bright!bright!
bright!bright!
bright!

• 迭代和优化

squares = [x**2 for x in [1,2,3,4,5]]
print(\'列表解析: {}\'.format(squares))

squares = []
for x in [1,2,3,4,5]:
    squares.append(x**2)
print(\'一般方法: {}\'.format(squares))

列表解析: [1, 4, 9, 16, 25]
一般方法: [1, 4, 9, 16, 25]

• 丢失键值

print(\'D: {}\'.format(D))

D[\'e\'] = 99 # # Assigning new keys grows dictionaries
print(\'D: {}\'.format(D))

try:
    D[\'f\'] ## Referencing a nonexistent key is an error
except:
    print(\'没有f这个键\')
    print(\'f\' in D)
    if not \'f\' in D:
        print(\'Missing\')

value = D.get(\'x\',0) # Index but with a default
print(\'value 1: {}\'.format(value))

value = D[\'x\'] if \'x\' in D else 0 # if/else expression form
print(\'value 2: {}\'.format(value))

D: {\'a\': 1, \'b\': 2, \'c\': 3}
D: {\'a\': 1, \'b\': 2, \'c\': 3, \'e\': 99}
没有f这个键
False
Missing
value 1: 0
value 2: 0

元组 = tuples

T = 1,2,3,4
print(\'Length: {}\'.format(len(T)))
print(\'Concatenation: {}\'.format(T+(5,6)))
print(\'the first element: {}\'.format(T[0]))
print(\'Tuple methods: 4 appears at offset 3: {}\'.format(T.index(4)))
print(\'# 4 appears once: {}\'.format(T.count(4)))
T = (\'spam\', 3.0, [11,22,33])
print(\'T[1]: {}\'.format(T[1]))
print(\'T[2][1]: {}\'.format(T[2][1]))

Length: 4
Concatenation: (1, 2, 3, 4, 5, 6)
the first element: 1
Tuple methods: 4 appears at offset 3: 3
# 4 appears once: 1
T[1]: 3.0
T[2][1]: 22

文件 = file

f = open(\'data.txt\', \'w\')# Make a new file in output mode
f.write(\'Hello\\n\')# Write strings of bytes to it
f.write(\'world\\n\')# Returns number of bytes written in Python 3.0
f.close() # Close to flush output buffers to disk

f = open(\'data.txt\')
text = f.read()
print(text)
print(\'file content is always a string: {}\'.format(text.split()))

Hello
world

file content is always a string: [\'Hello\', \'world\']

集合 = set

X = set(\'bright\')
Y = {\'b\', \'r\',\'t\',\'a\',\'z\'}
X,Y
print(\'X,Y: {}\'.format(X,Y))
print(\'X&Y: {}\'.format(X&Y))
print(\'X|Y: {}\'.format(X|Y))
print(\'X-Y: {}\'.format(X-Y))
print(\'Set comprehensions in 3.0: {}\'.format({x ** 2 for x in [1, 2, 3, 4]}))

X,Y: {\'g\', \'b\', \'t\', \'h\', \'i\', \'r\'}
X&Y: {\'b\', \'t\', \'r\'}
X|Y: {\'g\', \'b\', \'t\', \'h\', \'a\', \'i\', \'z\', \'r\'}
X-Y: {\'g\', \'h\', \'i\'}
Set comprehensions in 3.0: {16, 1, 4, 9}

小数与分数

1/3

0.3333333333333333

2/3 + 1/2

1.1666666666666665

import decimal
d = decimal.Decimal(\'3.141\')
print(\'d + 1 : {}\'.format(d+1))
decimal.getcontext().prec = 2
print(\'固定精度后的值: {}\'.format(decimal.Decimal(\'1.00\')/decimal.Decimal(\'3.00\')))

d + 1 : 4.141
固定精度后的值: 0.33

from fractions import Fraction
f = Fraction(2,3)
print(\'f+1: {}\'.format(f + 1))
f + Fraction(1,2)

f+1: 5/3





Fraction(7, 6)

参考《Learing Python》改编