if some_condition:
	# method1
	# method2
elif some_other_condition:
	#method3
	#method4
else:
	#method5
	#method6
#method7

>>> a=3;b=4;
>>> a
3
>>> b
4
>>> if a<b:
...     print('a<b')
... elif a==5:
...     print('a=5')
... else:
...     print('other')
... print('hello world')
... 
a<b
hello world
>>> a=5;b=2;
>>> if a<b:
...     print('a<b')
... elif a==5:
...     print('a=5')
... else:
...     print('other')
... print('hello world')
... 
a=5
hello world

#检查相等性
>>> 2==2
True
>>> 2==1
False
>>> 'hello'=='bye'
False
>>> 'hi'=='hi'
True
>>> 2=='2'
False
>>> 2.0==2 #数值
True
>>> 3!=3
False
>>> 4!=5
True
>>> 2>1
True
>>> 1>2
False
>>> 1<2
True
>>> 2<5
True
>>> 2>=2
True
>>> 4<=1
False

>>> 1<2
True
>>> 2<3
True
>>> 1<2<3 #直接串联
True
>>> 1<2>3
False
#使用逻辑运算符连接
 
>>> 1<2 and 2<3
True 
>>> 'h' == 'h' and 2==2
True
>>> ('h' == 'h') and (2==2)
True

>>> 1<2 && 2<3
  File "<python-input-23>", line 1
    1<2 && 2<3
         ^
SyntaxError: invalid syntax

#注意，这是按位与运算符，且优先级高于<，>
>>> 3 < 4 & 4 < 5  #相当于  3< (4&4) <5，3 < 4 < 5
True

>>> 1==1 or 2==2
True
>>> 100==1 or 2==2
True

>>> 1==1
True
>>> not(1==1)
False
>>> not 1==1
False
>>> not 400>5000
True
>>> 1!=1
False
>>> not 1==1 #相比1!=1，逻辑更清晰点  
False

%%writefile myfile.txt
Hello this is a text file
this is the second line
this is the third line

In [2]: %%writefile myfile_linux.txt
   ...: a
   ...: b
   ...: 
   ...: 
Overwriting myfile_linux.txt

(myenv) ly@dba13:~$ cat myfile_linux.txt
a
b

(myenv) ly@dba13:~$ cat myfile.txt #这个是我保存的jupyter编辑的文件
Hello this is a text file
this is the second line
this is the third line
(myenv) ly@dba13:~$ 

>>> [1,"2",3.5,['a','b']]
[1, '2', 3.5, ['a', 'b']]
>>> a=[1,"2",3.5,['a','b']]
>>> a[3]
['a', 'b']
>>> a[3][1]
'b'

>>> my_list=[1,2,3]
>>> my_list=['STRING',100,23.2]
>>> len(my_list)
3
>>> my_list[1:]
[100, 23.2]
>>> my_list[:1]
['STRING']
>>> mylist=['one','two','three']
>>> another_list=['four','five']
>>> mylist+another_list
['one', 'two', 'three', 'four', 'five']
>>> mylist
['one', 'two', 'three']
>>> another_list
['four', 'five']
>>> new_list=mylist+another_list
>>> new_list
['one', 'two', 'three', 'four', 'five']

>>> new_list[0]='One All Caps'
>>> new_list
['One All Caps', 'two', 'three', 'four', 'five']
>>> new_list.append('six') #向后添加元素
>>> new_list
['One All Caps', 'two', 'three', 'four', 'five', 'six']
>>> new_list[-1]='heihei' #修改最后一个元素
>>> new_list
['One All Caps', 'two', 'three', 'four', 'five', 'heihei']
>>> len(new_list)
6
>>> new_list[6]='heihei'  #向后添加元素不能用下标方式
Traceback (most recent call last):
  File "<python-input-23>", line 1, in <module>
    new_list[6]='heihei'
    ~~~~~~~~^^^
IndexError: list assignment index out of range
>>> new_list.pop
<built-in method pop of list object at 0x7f7a558dfb80>
#移除元素
>>> new_list.pop() #弹出并返回最后一个元素
'heihei'
>>> new_list
['One All Caps', 'two', 'three', 'four', 'five']
>>> popped_item=new_list.pop()
>>> popped_item
'five'
>>> new_list
['One All Caps', 'two', 'three', 'four']
#弹出指定索引的元素
>>> new_list
['One All Caps', 'two', 'three', 'four']
>>> new_list.pop(0)
'One All Caps'
>>> new_list
['two', 'three', 'four']
#弹出列表最后一个元素
>>> new_list.pop(-1)
'four'
>>> new_list
['two', 'three']

#接下来使用ipython

In [2]: print('hello')
hello

In [3]: print("Hello")
Hello

In [4]: print("I don't know")
I don't know

In [5]: print(' hah "hai"')
 hah "hai"

#返回字符串（不是打印字符串），所以这里还显示了''表示这是一个字符串
In [1]: 'hello'
Out[1]: 'hello'

In [2]: "world"
Out[2]: 'world'

In [3]: 'this is a "Test'
Out[3]: 'this is a "Test'

In [4]: 'this is a "Test"'
Out[4]: 'this is a "Test"'