python基础知识

学习python第一天笔记

2020.10.11
资料查询 for myself

输出语句

python没有int float等数据类型

print('welcome to python')

welcome to python

print('hello '+' world')

hello  world

print('i love u\n'*5)

i love u
i love u
i love u
i love u
i love u

输入语句

temp=input('please input a number:')
guess=int(temp)
if guess==3:
    print('equal me ^-^')
else:
    print('not equal me :)')

please input a number:1
not equal me :)

BIF=built in function 内置函数

dir(__builtins__)

['ArithmeticError',
 'AssertionError',
 'AttributeError',
 'BaseException',
 'BlockingIOError',
 'BrokenPipeError',
 'BufferError',
 'BytesWarning',
 'ChildProcessError',
 'ConnectionAbortedError',
 'ConnectionError',
 'ConnectionRefusedError',
 'ConnectionResetError',
 'DeprecationWarning',
 'EOFError',
 'Ellipsis',
 'EnvironmentError',
 'Exception',
 'False',
 'FileExistsError',
 'FileNotFoundError',
 'FloatingPointError',
 'FutureWarning',
 'GeneratorExit',
 'IOError',
 'ImportError',
 'ImportWarning',
 'IndentationError',
 'IndexError',
 'InterruptedError',
 'IsADirectoryError',
 'KeyError',
 'KeyboardInterrupt',
 'LookupError',
 'MemoryError',
 'ModuleNotFoundError',
 'NameError',
 'None',
 'NotADirectoryError',
 'NotImplemented',
 'NotImplementedError',
 'OSError',
 'OverflowError',
 'PendingDeprecationWarning',
 'PermissionError',
 'ProcessLookupError',
 'RecursionError',
 'ReferenceError',
 'ResourceWarning',
 'RuntimeError',
 'RuntimeWarning',
 'StopAsyncIteration',
 'StopIteration',
 'SyntaxError',
 'SyntaxWarning',
 'SystemError',
 'SystemExit',
 'TabError',
 'TimeoutError',
 'True',
 'TypeError',
 'UnboundLocalError',
 'UnicodeDecodeError',
 'UnicodeEncodeError',
 'UnicodeError',
 'UnicodeTranslateError',
 'UnicodeWarning',
 'UserWarning',
 'ValueError',
 'Warning',
 'WindowsError',
 'ZeroDivisionError',
 '__IPYTHON__',
 '__build_class__',
 '__debug__',
 '__doc__',
 '__import__',
 '__loader__',
 '__name__',
 '__package__',
 '__spec__',
 'abs',
 'all',
 'any',
 'ascii',
 'bin',
 'bool',
 'breakpoint',
 'bytearray',
 'bytes',
 'callable',
 'chr',
 'classmethod',
 'compile',
 'complex',
 'copyright',
 'credits',
 'delattr',
 'dict',
 'dir',
 'display',
 'divmod',
 'enumerate',
 'eval',
 'exec',
 'filter',
 'float',
 'format',
 'frozenset',
 'get_ipython',
 'getattr',
 'globals',
 'hasattr',
 'hash',
 'help',
 'hex',
 'id',
 'input',
 'int',
 'isinstance',
 'issubclass',
 'iter',
 'len',
 'license',
 'list',
 'locals',
 'map',
 'max',
 'memoryview',
 'min',
 'next',
 'object',
 'oct',
 'open',
 'ord',
 'pow',
 'print',
 'property',
 'range',
 'repr',
 'reversed',
 'round',
 'set',
 'setattr',
 'slice',
 'sorted',
 'staticmethod',
 'str',
 'sum',
 'super',
 'tuple',
 'type',
 'vars',
 'zip']

help(input)

Help on method raw_input in module ipykernel.kernelbase:

raw_input(prompt='') method of ipykernel.ipkernel.IPythonKernel instance
    Forward raw_input to frontends
    
    Raises
    ------
    StdinNotImplentedError if active frontend doesn't support stdin.

变量

python 没有“变量” 只有 ‘名字’

name='lifat'
print(name)
name='add lifat'
name

lifat





'add lifat'

first=1
second=3
print(first+second)

4

变量名可以包括字母、数字、下划线，但是不能以数字开头

字母可以大写也可以小写，python区分大小写

字符串

print('let\'s GO')

let's GO

print('C:\\now')

C:\now

原始字符串

st=r'let\n'
print(st)

let\n

st=r'let\'s go'#这里有一些问题
print(st)

let\'s go

三重引号

st="""I,
LOVE,
you.
"""
st

'I,\nLOVE,\nyou.\n'

print(st)

I,
LOVE,
you.

条件分支

if语句

if 1==1:
    print('dddddd')
else:
    print('bbbb')

dddddd

while循环

temp=input('please input a number:')
k=int(temp)
while k!=2:
    temp=input('please input a number:')
    k=int(temp)
   

please input a number:2

for循环

range()这个BIF可以使用

help(range)

Help on class range in module builtins:

class range(object)
 |  range(stop) -> range object
 |  range(start, stop[, step]) -> range object
 |  
 |  Return an object that produces a sequence of integers from start (inclusive)
 |  to stop (exclusive) by step.  range(i, j) produces i, i+1, i+2, ..., j-1.
 |  start defaults to 0, and stop is omitted!  range(4) produces 0, 1, 2, 3.
 |  These are exactly the valid indices for a list of 4 elements.
 |  When step is given, it specifies the increment (or decrement).
 |  
 |  Methods defined here:
 |  
 |  __bool__(self, /)
 |      self != 0
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(self, key, /)
 |      Return self[key].
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __hash__(self, /)
 |      Return hash(self).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __reduce__(...)
 |      Helper for pickle.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __reversed__(...)
 |      Return a reverse iterator.
 |  
 |  count(...)
 |      rangeobject.count(value) -> integer -- return number of occurrences of value
 |  
 |  index(...)
 |      rangeobject.index(value) -> integer -- return index of value.
 |      Raise ValueError if the value is not present.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  start
 |  
 |  step
 |  
 |  stop

两个关键语句

break 退出循环
continue 中止本轮循环

temp=input('please input a number:')
k=int(temp)
while k!=1:
    temp=input('please input a number:')
    k=int(temp)
    if k==4:
        break
    elif k==3:
        continue
    print('Test')
    

please input a number:2
please input a number:3
please input a number:2
Test
please input a number:5
Test
please input a number:4

python的数据类型

整型，布尔类型，浮点型，e记法

"520"+'das'

'520das'

a=150000000000000000
a

150000000000000000

15e10

150000000000.0

b=0.00000000000000002
b

2e-17

True+True

2

False+True

1

转化

int()
str()
float()

获得数据类型

type()
isinstance()

type("dddd")

str

a='ddddd'
isinstance(a,str)#这里判断str有问题,是因为上面用str去定义变量

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

TypeError                                 Traceback (most recent call last)

<ipython-input-150-dd385436226d> in <module>
      1 a='ddddd'
----> 2 isinstance(a,str)#这里判断str有问题,是因为上面用str去定义变量


TypeError: isinstance() arg 2 must be a type or tuple of types

help(str)

No Python documentation found for 'I,\nLOVE,\nyou.'.
Use help() to get the interactive help utility.
Use help(str) for help on the str class.

基本操作符

算术操作符

+ - * / ** // %

4**5

1024

9//2

4

9%2

1

逻辑操作符

and or not

not True

False

True and True

True

True and False

False

True or False

True

三元操作符

x=4
y=3
small = x if x<y else y
small

3

断言（assert）

当关键字后面的条件为假得到时候，程序自动崩溃并且抛出AssertionError

本文地址：https://blog.csdn.net/li_fat/article/details/109035816