python学习笔记

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使用的是anaconda带的spyder，一体化做的很方便。课程是南大等的笔记

python笔记

1.0 输入输出

input 输入
eval() 函数用来执行一个字符串表达式，并返回表达式的值。此处转换为int或元组，好处显而易见，当你只输入34时，eval帮你转化为整型，当你输入3，4时，eval把它转化为元组。就不用int或者tuple强制转换了，因为不确定你输入的是什么

In [13]：type(eval(input()))
"string","34"
Out[13]: tuple

In [15]：type(eval(input()))
"laove"
Out[15]: str

In [11]：type(eval(input()))
3
Out[11]: int

price = input('input the stock price of Apple: ')
input the stock price of Apple: 109
>>> price
'109'
>>> type(price)
<class 'str'>
>>> price = int(input('input the stock price of Apple: '))
>>> price = eval(input('input the stock price of Apple: '))

#input的输入是一个字符串。
#注意，利用input输入多个数时整数时,前面需要添加eval函数，参数直接用'，'分开。
y,z=eval(input("请输入2个整数，中间用逗号分开："))

请输入2个整数，中间用逗号分开：123, 222

n,m=input("请输入2个字符串，中间用逗号分开：").split(',')

请输入2个字符串，中间用逗号分开：asf, fsf

print(n, m)
asf  fsf

print 输出

>>> myString = 'Hello, World!'
>>> print(myString)
Hello, World!

>>> # variable
>>> p = 3.14159
>>> myString = 'is a mathematic circular constant'
>>> print(p, myString)
3.14159 is a mathematic circular constant

# print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

默认用“ ”连接输出，也可以更改print中的sep，用其他连接方式
print(变量）
print(字符串)
在这里插入图片描述

1.1 字符串

python中定义变量接收字符串，可以用单引号’，双引号“，当字符串中出现单引号，可以在前面加转义字符” \ “，或者字符串用三引号接受

>>> message = "Meet me tonight"
>>> print(message)
Meet me tonight
>>> message = 'The clock strikes at midnight'
>>> print(message)
The clock strikes at midnight
>>> message = " I'm looking for someone to share in an adventure"
>>> print(message)
 I'm looking for someone to share in an adventure
>>> message  = ''' That's too bad'''
>>> print(message);
 That's too bad
>>> movie_quote = """ One of my favorite lines from Godfather is :
... " I'm going to make him an offer he can't refuse. "
... Do you know who said this? """
>>> print(movie_quote)
 One of my favorite lines from Godfather is :
" I'm going to make him an offer he can't refuse. "
Do you know who said this?

字符串的format输出和，字符串前用的r，u， f，等

sumA = 0
i = 1
while True:
sumA += i
i += 1
if sumA > 10:
break
print('i={},sum={}'.format(i, sumA))
print(f'i={i},sum={sumA}')

1.2 基本数据类型

不可变类型，内存中的数据不允许被修改：
- 数字类型 int, bool, float, complex, long(2.x)
- 字符串 str
- 元组 tuple
可变类型，内存中的数据可以被修改：
- 列表 list
- 字典 dict
Python 中数据类型还可以分为数字型和非数字型
- 数字型
  - 整型 (int)
  - 浮点型（float）
  - 布尔型（bool）真 True 假 False 0—— 非零即真
  - 复数型 (complex) 主要用于科学计算，例如：平面场问题、波动问题、电感电容等问题
- 非数字型
  - 字符串列表元组字典
在 Python 中，所有非数字型变量都支持以下特点：

都是一个序列 sequence，也可以理解为容器
取值 []
遍历 for in
计算长度、最大/最小值、比较、删除
链接 + 和重复 *
切片

1.2.1 python2

types of numbers: int , long, float, complex
type() 可以用来查看变量类型
#用来表示注释
python会自动转型，int->long->float->complex

>>> # everything after a hash tag is a comment and is ignored by the interpreter
>>> a = 28
>>> type(a)
<type 'int'>
>>> a
28
>>> print(a)
28
>>>	# c = 10l
>>> c = 10L 
>>> type(c)
<type 'long'>
>>> e = 2.71821828
>>> type(e)
<type 'float'>
>>> # complex包括实部和虚部，real表示实部，imaginary表示虚部属性
>>> z = 3 + 5.7j
>>> type(z)
<type 'complex'>
>>> z.real
3.0
>>> z.imag
5.7

1.2.2 python3 关键字和表达式

Types of numbers: int, float, numbers
不用担心溢出问题，python也会自动转型

1.3 算术运算符

1.3.1 Arithmetic in python2

Numbers: int, long, float, complex
Four operations: add subtract multiply and divide (+,-,*,/)
The idea of narrower and wider types

>>> x = 5 # int
>>> y = 5L # long
>>> y
5L
>>> long(5)
5L
>>> z = long(y)
>>> z
5L
>>> z = long(x)
>>> z
5L
>>> x
5
>>> # ints are narrower than longs
... # longs are wider than ints
...
>>> # To convert a long to float just add a point 0 at the end
...
>>> x = 28L
>>> y = 28.0 # float
>>> z = float(28)

>>> x = 1.732
>>> 1.732 + 0j
(1.732+0j)
>>> complex(1.732)
(1.732+0j)
>>> float(1.732+0j)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't convert complex to float

>>> a = 2 # int
>>> b = 3L # long
>>> c = 6.0 # float
>>> d = 12 + 0j #complex
>>> # Rule : Widen numbers so they're the same type
...
>>> #Addition
... a + b # int + long
5L
>>> # Subtraction
... c - b # float - long
3.0
>>> # Multiplication
... a * c # int * float
12.0
>>> # Division
... d / c # complex / float
(2+0j)

>>> 16/5
3
>>> 16%5
1
>>> # 在python2中16/5 得到 Quotient ，  16%5 得到Remainder  ，0不能为除数
... # 在python3中16/5 得到3.2，转型为float类型

1.3.2 Arthmetic in python3

types of numbers: int, float, complex
Operations: Addition Subtraction Multiplication Division

>>> x = 28
>>> x = 28 # int
>>> y = 28.0 # float
>>> float(28)
28.0
>>> z = float(x)
>>> z
28.0
>>> x #并没有改变x本身的类型
28
>>> 3.14 # float
3.14
>>> int(3.14) # 四舍五入成整数
3

>>> a = 2 # int
>>> b = 6.0 # float
>>> c = 12 +0j #complex number
>>> # Rule : Widen numbers so they're the same type
...
>>> # Addition
... a + b # int + float
8.0
>>> # Subtraction
... b - a # float - int
4.0
>>> # Multiplication
... a * 7 # int * int
14
>>> # Division
... c / b # complex / float
(2+0j)
>>> # 都是向更高范围转型
>>> 16/3 # 返回浮点型数据
5.333333333333333
>>> 16//3 # Quotient
5
>>> 16%3 # Remainder
1

1.4 Pythons interactive help features (dir and help)

>>> dir() # Short for "directory", Python displays a list of available objects When you press Enter
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__']
>>> dir(__builtins__)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError', '...]
>>> help(pow)
# the first line confirms it is a function in the __builtin__ module
Help on built-in function pow in module builtins:

# the following lines show how to use the funtion, there are 3 inputs listed x, y, z
pow(x, y, z=None, /)
    Equivalent to x**y (with two arguments) or x**y % z (with three arguments)

    Some types, such as ints, are able to use a more efficient algorithm when
    invoked using the three argument form.

>>> pow(2,10)
1024
>>> pow(2,10,3)
1
>>> 2**10
1024
>>> 2**10%3
1

用dir()显示的模块都是默认不需要导入的，如__builtins__,模块，可以用help查看其中的函数使用，用help还可以查找其他模块，help(‘modules’)

>>> help('modules')

Please wait a moment while I gather a list of all available modules...

__future__          _tkinter            glob                runpy
_abc                _tracemalloc        grp                 sched
_ast                _uuid               gzip                secrets
_asyncio            _warnings           hashlib             select
_bisect             _weakref            heapq               selectors
_blake2             _weakrefset         hello               setuptools
_bootlocale         _xxtestfuzz         hmac                shelve
_bz2 ...               
>>> import math
>>> dir() # 确定库，是否导入成功
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'math']
>>> dir(math)
['__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'inf', 'isclose', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'nan', 'pi', 'pow', 'radians', 'remainder', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'tau', 'trunc']
>>> math.sin(3.1415926/3)
0.8660253948528064
>>> math.sin(1)
0.8414709848078965
>>> help(radians)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'radians' is not defined
>>> help(math.radians)
Help on built-in function radians in module math:

radians(x, /)
    Convert angle x from degrees to radians.

>>> math.sin(math.radians(60)) #角度转化为弧度值
0.8660254037844386
>>> math.sin(math.radians(30))
0.49999999999999994

1.5 True or False

0 is False while 1 is True

>>> True
True
>>> true
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'true' is not defined
>>> False
False
>>> 3 == 5
False


>>> str(True) # convert it to string
'True'
>>> int(True)
1
>>> 5 + True
6

1.6 datetime 操练

>>> dir() # 先看没有datetime模块
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'math']
>>> help('modules') # 查看所有模块

Please wait a moment while I gather a list of all available modules...
x
__future__          _tkinter            glob                runpy
_abc                _tracemalloc        grp                 sched
_ast ...          

>>> import datetime  # 导入datetime模块
>>> dir() # 查看是否导入成功
['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'datetime', 'math']

>>> dir(datetime)  # 查看datetime模块中类、属性等，包含date，time，datetime等类
['MAXYEAR', 'MINYEAR', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'date', 'datetime', 'datetime_CAPI', 'time', 'timedelta', 'timezone', 'tzinfo']

>>> gvr = datetime.date(1956,1, 31)
>>> gvr
datetime.date(1956, 1, 31)
>>> print(gvr)
1956-01-31
>>> print(gvr.year)
1956
>>> print(gvr.month)
1
>>> print(gvr.max)
9999-12-31
>>> print(gvr.day)
31


>>> dt = datetime.timedelta(100) # timedelta类可用来修改日期的，正数代表加100天，负数（-100）代表减100天
>>> dt
datetime.timedelta(days=100)
>>> print(dt)
100 days, 0:00:00
>>> mill = datetime.date(2000,1,1)
>>> print(mill+dt)
2000-04-10

>>> #python Default format： yyyy-mm-dd,but you can specify a different format if you like

>>> print(gvr.strftime("%A, %B, %d, %Y")) # %A is the full name of the day(周几),%B month,%d, is the day of the month and %Y is the four-digit year
Tuesday, January, 31, 1956

>>> message  =  "GVR was born on {:%A, %B, %d, %Y}."
>>> print(message.format(gvr))
GVR was born on Tuesday, January, 31, 1956.

>>> launch_date = datetime.date(2017,3,30)
>>> launch_time = datetime.time(22,27,0)
>>> launch_datetime = datetime.datetime(2017,3,20,22,27,0)
>>> print(launch_date)
2017-03-30
>>> print(launch_time)
22:27:00
>>> print(launch_datetime)
2017-03-20 22:27:00
>>> print(launch_datetime.hour)
22

# 获取当前时间
>>> now  = datetime.datetime.today()
>>> print(now)
2020-01-20 18:20:55.425133
>>> print(now.microsecond)
425133



# 把时间字符串转换为时间对象
>>> moon_landing  = "7/20/1969"
>>> moon_landing_datetime = datetime.datetime.strptime(moon_landing,"%m/%d/%Y")
>>> print(moon_landing)
7/20/1969
>>> print(moon_landing_datetime)
1969-07-20 00:00:00
>>> print(type(moon_landing_datetime))
<class 'datetime.datetime'>

在这里插入图片描述

1.7 条件、循环和函数

1.7.1 小练习：输出2-100直接的素数

for循环格式

iterable_object为可迭代对象
判断是否为迭代器（Iterator）和可迭代对象（Iterable）

from collections.abc import Iterator, Iterable

isinstance(range(10), Iterator)
Out[14]: False

isinstance(iter(range(10)), Iterator)
Out[15]: True

isinstance(range(10), Iterable)
Out[17]: True

# 迭代器用next访问下一个元素
x = iter(range(3))

next(x)
Out[24]: 0

next(x)
Out[25]: 1

next(x)
Out[26]: 2

next(x)
Traceback (most recent call last):

  File "<ipython-input-27-92de4e9f6b1e>", line 1, in <module>
    next(x)

StopIteration

String, List, Tuple,Dictionary, File

for iter_var in iterable_object:
	suite_to repeat
# 直接访问字符串
s = "Python"

for x in s:
    print(x, end=" ")
    
P y t h o n 
# 索引方式访问字符串
for x in range(len(s)):
    print(s[x], end=" ")
    
P y t h o n

for循环判断素数

import math
def isPrime():
    primeList = []
    for item in range (2,101):
        for x in range(2, int(math.sqrt(item))+1):
            if item%x == 0 and item != x:
                print(f"{item} is not prime")
                break
        else:
            primeList.append(item)
            print(f"{item} is prime")
    print(primeList)
isPrime()

输出：[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

while循环格式

j = 1
sum = 0
while j<10:
	sum += j
	j+=1

1.7.2 条件语句缩减

x>0 则 t=1 否则 t=0

t = 1 if x> 0 else 0

1.7.3 一些函数的使用

1.7.3.1 range()

返回的是a 到 b-1的列表对象，c是步长

# 默认start也是0
range(start, end , step=1)
range(start, end)
range(end)

>>> list(range(3, 11, 2))
[3, 5, 7, 9]
#一共11-3 = 8 个元素的列表
list(range(3, 11))
Out[1]: [3, 4, 5, 6, 7, 8, 9, 10]
#一共11-0 = 11 个元素的列表
list(range(11))
Out[2]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

1.7.3.2 enumerate()

1.8 异常

在这里插入图片描述

—小例子

# 保留字符串中的字母
coffeeList = ["32Latte", "_Americano30", "/34Cappuccino", "Mocha35"]
def cleanList(lst):
    cleanedList = []
    for item in lst:
        for u in item:
            if u.isalpha() != True:
                item = item.replace(u,"")
        cleanedList.append(item)
    return cleanedList
print(cleanList(coffeeList))

# 这里是出错代码
def cleanList(lst):
    cleanedList = []
    for item in lst:
        itemCopy = item[:]
        for u in item:
            if u.isalpha() != True:
                itemCopy = itemCopy.strip(u) #删除会引起item的改变，需要再次循环多一个item【】副本
        cleanedList.append(itemCopy)
    return cleanedList