ML - Python 基础

作者: leo567 | 来源:发表于2018-10-10 15:10 被阅读26次

数据类型 Numeric & String

1. Python数据类型

1.1 总体：numerics, sequences, mappings, classes, instances, and exceptions

1.2 Numeric Types: int (包含boolean), float, complex

1.3 int: unlimited length; float: 实现用double in C, 可查看 sys.float_info; complex: real(实部) & imaginary(虚部）,用z.real 和 z.imag来取两部分

1.4 具体运算以及法则参见：https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex


import sys

a = 3

b = 4

c = 5.66

d = 8.0

e = complex(c, d)

f = complex(float(a), float(b))

print (*"a is type"* , type(a))

print (*"b is type"* , type(b))

print (*"c is type"* , type(c))

print (*"d is type"* , type(d))

print (*"e is type"* , type(e))

print (*"f is type"* , type(f))

print(a + b)

print(d / c)

print (b / a)

print (b // a)

print (e)

print (e + f)

print (*"e's real part is: "* , e.real)

print (*"e's imaginary part is: "* , e.imag)

print (sys.float_info)

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
a is type <class 'int'>
b is type <class 'int'>
c is type <class 'float'>
d is type <class 'float'>
e is type <class 'complex'>
f is type <class 'complex'>
7
1.4134275618374559
1.3333333333333333
1
(5.66+8j)
(8.66+12j)
e's real part is:  5.66
e's imaginary part is:  8.0
sys.float_info(max=1.7976931348623157e+308, max_exp=1024, max_10_exp=308, min=2.2250738585072014e-308, min_exp=-1021, min_10_exp=-307, dig=15, mant_dig=53, epsilon=2.220446049250313e-16, radix=2, rounds=1)

Process finished with exit code 0

字符串(String)&变量 (Variable)

字符串：
一串字符
显示或者打印出来文字信息
导出
编码：# -- coding: utf-8 --
单引号，双引号，三引号
不可变（immutable)
Format字符串
age = 3
name = "Tom"
print("{0} was {1} years old".format(name, age))
联合：+: print(name + " was " + str(age) + " years old")
换行符: print("What's your name? \nTom")
字面常量（literal constant):

可以直接以字面的意义使用它们：
如：6，2.24，3.45e-3, "This is a string"
常量：不会被改变

变量：
储存信息
属于identifier
identifier命名规则：
第一个字符必须是字母或者下划线
其余字符可以是字母，数字，或者下划线
区分大小写
如：合法：i, name_3_4, big_bang
不合法：2people, this is tom, my-name, >123b_c2

注释： #
缩进(Indentation)

数据结构：列表（List）

print中的编码：
编码：# -- coding: utf-8 --
print中的换行
print("What's your name? \nTom")
List
创建
访问
更新
删除
脚本操作符
函数方法

  # -*- coding: utf-8 -*-

 #创建一个列表
 
 number_list = [1, 3, 5, 7, 9]

 string_list = ["abc", "bbc", "python"]
 
 mixed_list = ['python', 'java', 3, 12]
 
 #访问列表中的值
 
 second_num = number_list[1]
 
 third_string = string_list[2]
 
 fourth_mix = mixed_list[3]
 
 print("second_num: {0} third_string: {1} fourth_mix: {2}".format(second_num, third_string, fourth_mix))
 
 #更新列表
 
 print("number_list before: " + str(number_list))
 
 number_list[1] = 30
 
 print("number_list after: " + str(number_list))
 
 #删除列表元素
 
 print("mixed_list before delete: " + str(mixed_list))
 
 del mixed_list[2]
 
 print("mixed_list after delete: " + str(mixed_list))
 
 #Python脚本语言
 
 print(len([1,2,3])) #长度
 
 print([1,2,3] + [4,5,6]) #组合

 print(['Hello'] * 4) #重复

 print(3 in [1,2,3]) #某元素是否在列表中
 
 #列表的截取
 
 abcd_list =['a', 'b', 'c', 'd'] 
 
 print(abcd_list[1])
 
 print(abcd_list[-2])
 
 print(abcd_list[1:])

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
second_num: 3 third_string: python fourth_mix: 12
number_list before: [1, 3, 5, 7, 9]
number_list after: [1, 30, 5, 7, 9]
mixed_list before delete: ['python', 'java', 3, 12]
mixed_list after delete: ['python', 'java', 12]
3
[1, 2, 3, 4, 5, 6]
['Hello', 'Hello', 'Hello', 'Hello']
True
b
c
['b', 'c', 'd']

Process finished with exit code 0

列表操作包含以下函数:
1、cmp(list1, list2)：比较两个列表的元素
2、len(list)：列表元素个数
3、max(list)：返回列表元素最大值
4、min(list)：返回列表元素最小值
5、list(seq)：将元组转换为列表
列表操作包含以下方法:
1、list.append(obj)：在列表末尾添加新的对象
2、list.count(obj)：统计某个元素在列表中出现的次数
3、list.extend(seq)：在列表末尾一次性追加另一个序列中的多个值（用新列表扩展原来的列表）
4、list.index(obj)：从列表中找出某个值第一个匹配项的索引位置
5、list.insert(index, obj)：将对象插入列表
6、list.pop(obj=list[-1])：移除列表中的一个元素（默认最后一个元素），并且返回该元素的值
7、list.remove(obj)：移除列表中某个值的第一个匹配项
8、list.reverse()：反向列表中元素
9、list.sort([func])：对原列表进行排序

tuple(元组)

创建只有一个元素的tuple，需要用逗号结尾消除歧义
a_tuple = (2,)

tuple中的list

mixed_tuple = (1, 2, ['a', 'b'])

print("mixed_tuple: " + str(mixed_tuple))

mixed_tuple[2][0] = 'c'
mixed_tuple[2][1] = 'd'

print("mixed_tuple: " + str(mixed_tuple))

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
mixed_tuple: (1, 2, ['a', 'b'])
mixed_tuple: (1, 2, ['c', 'd'])

Process finished with exit code 0

Tuple 是不可变 list。一旦创建了一个 tuple 就不能以任何方式改变它。

Tuple 与 list 的相同之处
定义 tuple 与定义 list 的方式相同, 除了整个元素集是用小括号包围的而不是方括号。
Tuple 的元素与 list 一样按定义的次序进行排序。 Tuples 的索引与 list 一样从 0 开始, 所以一个非空 tuple 的第一个元素总是 t[0]。
负数索引与 list 一样从 tuple 的尾部开始计数。
与 list 一样分片 (slice) 也可以使用。注意当分割一个 list 时, 会得到一个新的 list ；当分割一个 tuple 时, 会得到一个新的 tuple。

Tuple 不存在的方法
您不能向 tuple 增加元素。Tuple 没有 append 或 extend 方法。
您不能从 tuple 删除元素。Tuple 没有 remove 或 pop 方法。
然而, 您可以使用 in 来查看一个元素是否存在于 tuple 中。

用 Tuple 的好处
Tuple 比 list 操作速度快。如果您定义了一个值的常量集，并且唯一要用它做的是不断地遍历它，请使用 tuple 代替 list。
如果对不需要修改的数据进行 “写保护”，可以使代码更安全。使用 tuple 而不是 list 如同拥有一个隐含的 assert 语句，说明这一数据是常量。如果必须要改变这些值，则需要执行 tuple 到 list 的转换。

Tuple 与 list 的转换
Tuple 可以转换成 list，反之亦然。内置的 tuple 函数接收一个 list，并返回一个有着相同元素的 tuple。而 list 函数接收一个 tuple 返回一个 list。从效果上看，tuple 冻结一个 list，而 list 解冻一个 tuple。

Tuple 的其他应用
一次赋多值
v = ('a', 'b', 'e')
(x, y, z) = v
解释：v 是一个三元素的 tuple, 并且 (x, y, z) 是一个三变量的 tuple。将一个 tuple 赋值给另一个 tuple, 会按顺序将 v 的每个值赋值给每个变量。

字典 (Dictionary)

字典内置函数&方法( 键(key)，对应值(value))

Python字典包含了以下内置函数：

1、cmp(dict1, dict2)：比较两个字典元素。

2、len(dict)：计算字典元素个数，即键的总数。

3、str(dict)：输出字典可打印的字符串表示。

4、type(variable)：返回输入的变量类型，如果变量是字典就返回字典类型。

Python字典包含了以下内置方法：

1、radiansdict.clear()：删除字典内所有元素

2、radiansdict.copy()：返回一个字典的浅复制

3、radiansdict.fromkeys()：创建一个新字典，以序列seq中元素做字典的键，val为字典所有键对应的初始值

4、radiansdict.get(key, default=None)：返回指定键的值，如果值不在字典中返回default值

5、radiansdict.has_key(key)：如果键在字典dict里返回true，否则返回false

6、radiansdict.items()：以列表返回可遍历的(键, 值) 元组数组

7、radiansdict.keys()：以列表返回一个字典所有的键

8、radiansdict.setdefault(key, default=None)：和get()类似, 但如果键不已经存在于字典中，将会添加键并将值设为default

9、radiansdict.update(dict2)：把字典dict2的键/值对更新到dict里

10、radiansdict.values()：以列表返回字典中的所有值

 # -*- coding: utf-8 -*-

#创建一个词典

phone_book = {'Tom': 123, "Jerry": 456, 'Kim': 789}

mixed_dict = {"Tom": 'boy', 11: 23.5}

#访问词典里的值

print("Tom's number is " + str(phone_book['Tom']))

print('Tom is a ' + mixed_dict['Tom'])

#修改词典

phone_book['Tom'] = 999

phone_book['Heath'] = 888

print("phone_book: " + str(phone_book)) 

phone_book.update({'Ling':159, 'Lili':247})

print("updated phone_book: " + str(phone_book)) 

#删除词典元素以及词典本身

del phone_book['Tom']

print("phone_book after deleting Tom: " + str(phone_book)) 

#清空词典

phone_book.clear()

print("after clear: " + str(phone_book))

#删除词典

del phone_book

# print("after del: " + str(phone_book))

#不允许同一个键出现两次

rep_test = {'Name': 'aa', 'age':5, 'Name': 'bb'}

print("rep_test: " + str(rep_test))

#键必须不可变，所以可以用数，字符串或者元组充当，列表不行

list_dict = {['Name']: 'John', 'Age':13}

list_dict = {('Name'): 'John', 'Age':13}

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
Tom's number is 123
Tom is a boy
phone_book: {'Tom': 999, 'Jerry': 456, 'Kim': 789, 'Heath': 888}
updated phone_book: {'Tom': 999, 'Jerry': 456, 'Kim': 789, 'Heath': 888, 'Ling': 159, 'Lili': 247}
phone_book after deleting Tom: {'Jerry': 456, 'Kim': 789, 'Heath': 888, 'Ling': 159, 'Lili': 247}
after clear: {}
rep_test: {'Name': 'bb', 'age': 5}
Traceback (most recent call last):
  File "D:/python/untitled1/note08.py", line 46, in <module>
    list_dict = {['Name']: 'John', 'Age':13}
TypeError: unhashable type: 'list'

Process finished with exit code 1

函数

函数：程序中可重复使用的程序段

给一段程程序起一个名字，用这个名字来执行一段程序，反复使用（调用函数）

用关键字 ‘def' 来定义，identifier(参数)

identifier

参数list

return statement

局部变量 vs 全局变量

# -*- coding: utf-8 -*-

#没有参数和返回的函数
def say_hi():
    print(" hi!")

say_hi()
say_hi()


#有参数，无返回值
def print_sum_two(a, b):
    c = a + b
    print(c)

print_sum_two(3, 6)

def hello_some(str):
    print("hello " + str + "!")

hello_some("China")
hello_some("Python")


#有参数，有返回值
def repeat_str(str, times):
    repeated_strs = str * times
    return repeated_strs


repeated_strings = repeat_str("Happy Birthday!", 4)
print(repeated_strings)


#全局变量与局部 变量
x = 60

def foo(x):
    print("x is: " + str(x))
    x = 3
    print("change local x to " + str(x))

foo(x)
print('x is still', str(x))


x = 60


def foo():
    global x
    print("x is: " + str(x))
    x = 3
    print("change local x to " + str(x))


foo()
print('value of x is', str(x))

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
 hi!
 hi!
9
hello China!
hello Python!
Happy Birthday!Happy Birthday!Happy Birthday!Happy Birthday!
x is: 60
change local x to 3
x is still 60
x is: 60
change local x to 3
value of x is 3

Process finished with exit code 0

默认参数

关键字参数

VarArgs参数


# -*- coding: utf-8 -*-

# 默认参数
def repeat_str(s, times=1):
    repeated_strs = s * times
    return repeated_strs


repeated_strings = repeat_str("Happy Birthday!")
print(repeated_strings)

repeated_strings_2 = repeat_str("Happy Birthday!", 4)
print(repeated_strings_2)


# 不能在有默认参数后面跟随没有默认参数
# f(a, b =2)合法
# f(a = 2, b)非法

# 关键字参数: 调用函数时，选择性的传入部分参数
def func(a, b=4, c=8):
    print('a is', a, 'and b is', b, 'and c is', c)


func(13, 17)
func(125, c=24)
func(c=40, a=80)


# VarArgs参数
def print_paras(fpara, *nums, **words):
    print("fpara: " + str(fpara))
    print("nums: " + str(nums))
    print("words: " + str(words))


print_paras("hello", 1, 3, 5, 7, word="python", anohter_word="java")

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
Happy Birthday!
Happy Birthday!Happy Birthday!Happy Birthday!Happy Birthday!
a is 13 and b is 17 and c is 8
a is 125 and b is 4 and c is 24
a is 80 and b is 4 and c is 40
fpara: hello
nums: (1, 3, 5, 7)
words: {'word': 'python', 'anohter_word': 'java'}

Process finished with exit code 0

控制流：if & for 语句

if 语句

if condition:
do something
elif other_condition:
do something

for 语句


# -*- coding: utf-8 -*-


#if statement example

number = 59
guess = int(input('Enter an integer : '))

if guess == number:
    # New block starts here
    print('Bingo! you guessed it right.')
    print('(but you do not win any prizes!)')
    # New block ends here
elif guess < number:
    # Another block
    print('No, the number is higher than that')
    # You can do whatever you want in a block ...
else:
    print('No, the number is a  lower than that')
    # you must have guessed > number to reach here

print('Done')
# This last statement is always executed,
# after the if statement is executed.


#the for loop example

for i in range(1, 10):
    print(i)
else:
    print('The for loop is over')


a_list = [1, 3, 5, 7, 9]
for i in a_list:
    print(i)

a_tuple = (1, 3, 5, 7, 9)
for i in a_tuple:
    print(i)

a_dict = {'Tom':'111', 'Jerry':'222', 'Cathy':'333'}
for ele in a_dict:
    print(ele)
    print(a_dict[ele])

for key, elem in a_dict.items():
    print(key, elem)

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
Enter an integer : 77
No, the number is a  lower than that
Done
1
2
3
4
5
6
7
8
9
The for loop is over
1
3
5
7
9
1
3
5
7
9
Tom
111
Jerry
222
Cathy
333
Tom 111
Jerry 222
Cathy 333

Process finished with exit code 0

控制流：while & range语句


# -*- coding: utf-8 -*-


number = 59
guess_flag = False


while guess_flag == False:
    guess = int(input('Enter an integer : '))
    if guess == number:
        # New block starts here
        guess_flag = True

        # New block ends here
    elif guess < number:
        # Another block
        print('No, the number is higher than that, keep guessing')
        # You can do whatever you want in a block ...
    else:
        print('No, the number is a  lower than that, keep guessing')
        # you must have guessed > number to reach here

print('Bingo! you guessed it right.')
print('(but you do not win any prizes!)')
print('Done')

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
Enter an integer : 66
No, the number is a  lower than that, keep guessing
Enter an integer : 38
No, the number is higher than that, keep guessing
Enter an integer : 59
Bingo! you guessed it right.
(but you do not win any prizes!)
Done

Process finished with exit code 0


# -*- coding: utf-8 -*-



number = 59
num_chances = 3
print("you have only 3 chances to guess")

for i in range(1, num_chances + 1):
    print("chance " + str(i))
    guess = int(input('Enter an integer : '))
    if guess == number:
        # New block starts here
        print('Bingo! you guessed it right.')
        print('(but you do not win any prizes!)')
        break

        # New block ends here
    elif guess < number:
        # Another block
        print('No, the number is higher than that, keep guessing, you have ' + str(num_chances - i) + ' chances left')
        # You can do whatever you want in a block ...
    else:
        print('No, the number is lower than that, keep guessing, you have ' + str(num_chances - i) + ' chances left')
        # you must have guessed > number to reach here


print('Done')

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
you have only 3 chances to guess
chance 1
Enter an integer : 55
No, the number is higher than that, keep guessing, you have 2 chances left
chance 2
Enter an integer : 69
No, the number is lower than that, keep guessing, you have 1 chances left
chance 3
Enter an integer : 23
No, the number is higher than that, keep guessing, you have 0 chances left
Done

Process finished with exit code 0

控制流：break, continue & pass

1. break

2. continue

3. pass


number = 59

while True:
    guess = int(input('Enter an integer : '))
    if guess == number:
        # New block starts here
        break

        # New block ends here
    if guess < number:
        # Another block
        print('No, the number is higher than that, keep guessing')
        continue
        # You can do whatever you want in a block ...
    else:
        print('No, the number is a  lower than that, keep guessing')
        continue
        # you must have guessed > number to reach here

print('Bingo! you guessed it right.')
print('(but you do not win any prizes!)')
print('Done')


a_list = [0, 1, 2]

print("using continue:")
for i in a_list:
    if not i:
        continue
    print(i)

print("using pass:")
for i in a_list:
    if not i:
        pass
    print(i)

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
Enter an integer : 23
No, the number is higher than that, keep guessing
Enter an integer : 59
Bingo! you guessed it right.
(but you do not win any prizes!)
Done
using continue:
1
2
using pass:
0
1
2

Process finished with exit code 0

输入输出方式介绍(Output Format)

 str_1 = input("Enter a string: ")

str_2 = input("Enter another string: ")

print("str_1 is: " + str_1 + ". str_2 is :" + str_2)

print("str_1 is {} + str_2 is {}".format(str_1, str_2))

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
Enter a string: fanrunqi
Enter another string: rookie
str_1 is: fanrunqi. str_2 is :rookie
str_1 is fanrunqi + str_2 is rookie

Process finished with exit code 0

读写文件

1. 写出文件

2. 读入文件

some_sentences = '''\
I love learning python
because python is fun
and also easy to use
'''

#Open for 'w'irting
f = open('sentences.txt', 'w')
#Write text to File
f.write(some_sentences)
f.close()

#If not specifying mode, 'r'ead mode is default
f = open('sentences.txt')
while True:
    line = f.readline()
    #Zero length means End Of File
    if len(line) == 0:
        break
    print(line)
# close the File
f.close

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
I love learning python

because python is fun

and also easy to use


Process finished with exit code 0

错误与异常处理(Error & Exceptions)

Python有两种错误类型：

1. 语法错误(Syntax Errors)

2. 异常（Exceptions)

首先，try语句下的（try和except之间的代码）被执行

如果没有出现异常，except语句将被忽略

如果try语句之间出现了异常，try之下异常之后的代码被忽略，直接跳跃到except语句

如果异常出现，但并不属于except中定义的异常类型，程序将执行外围一层的try语句，如果异常没有被处理，将产生unhandled exception的错误

处理异常（Handling Exceptions)

Exception doc: https://docs.python.org/3.4/library/exceptions.html

#Handling exceptions

while True:
    try:
        x = int(input("Please enter a number"))
        break
    except ValueError:
        print("Not valid input, try again...")

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
Please enter a numberfan
Not valid input, try again...
Please enter a numberrun
Not valid input, try again...
Please enter a numberqi
Not valid input, try again...
Please enter a number7

Process finished with exit code 0

面向对象编程(Object-Oriented)和装饰器(decorator)

1. 面向对象编程

Python支持面向对象编程

类(class)：现实世界中一些事物的封装（如：学生）

类：属性（如：名字，成绩）

类对象

实例对象

引用：通过引用对类的属性和方法进行操作

实例化：创建一个类的具体实例对象（如：学生张三）

2. 装饰器(decorator)

 class Student:

    def __init__(self, name, grade):

        self.name = name

        self.grade = grade

    def introduce(self):

        print("hi! I'm " + self.name)

        print("my grade is: " + str(self.grade))

    def improve(self, amount):

        self.grade = self.grade + amount

jim = Student("jim", 86)

jim.introduce()

jim.improve(10)

jim.introduce()

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
hi! I'm jim
my grade is: 86
hi! I'm jim
my grade is: 96

Process finished with exit code 0

def add_candles(cake_func):
    def insert_candles():
        return cake_func() + " candles"
    return insert_candles

def make_cake():
    return "cake"

gift_func = add_candles(make_cake)

print(make_cake())
print(gift_func())





def add_candles(cake_func):
    def insert_candles():
        return cake_func() + " candles"
    return insert_candles

def make_cake():
    return "cake"

make_cake = add_candles(make_cake)

print(make_cake())
# print(gift_func)




def add_candles(cake_func):
    def insert_candles():
        return cake_func() + " and candles"
    return insert_candles

@add_candles
def make_cake():
    return "cake"

# make_cake = add_candles(make_cake)

print(make_cake())
# print(gift_func)

D:\Anaconda3\python.exe D:/python/untitled1/note08.py
cake
cake candles
cake candles
cake and candles

Process finished with exit code 0

图形界面（GUI）

1. GUI： Graphical User Interface

2. tkinter: GUI library for Python

3. GUI Example

# -*- coding: utf-8 -*-

from tkinter import *

import tkinter.simpledialog as dl
import tkinter.messagebox as mb

# tkinter GUI Input Output Example
# 设置GUI
root = Tk()
w = Label(root, text="Label Title")
w.pack()

# 欢迎消息
mb.showinfo("Welcome", "Welcome Message")
guess = dl.askinteger("Number", "Enter a number")

output = 'This is output message'
mb.showinfo("Output: ", output)

猜数字游戏

# -*- coding: utf-8 -*-

from tkinter import *

import tkinter.simpledialog as dl
import tkinter.messagebox as mb

root = Tk()
w = Label(root, text = "Guess Number Game")
w.pack()

#欢迎消息
mb.showinfo("Welcome", "Welcome to Guess Number Game")


#处理信息
number = 59

while True:
#让用户输入信息
    guess = dl.askinteger("Number", "What's your guess?")

    if guess == number:
        # New block starts here
        output = 'Bingo! you guessed it right, but you do not win any prizes!'
        mb.showinfo("Hint: ", output)
        break
        # New block ends here
    elif guess < number:
        output = 'No, the number is a  higer than that'
        mb.showinfo("Hint: ", output)
    else:
        output = 'No, the number is a  lower than that'
        mb.showinfo("Hint: ", output)

print('Done')