module

a python file is a module

use import to import module:

ex:

import  test

this will import test.py

a module is imported only once per process by default. Further imports reuse loaded modules in memory

use sys.modules.keys() to find loaded module

when module is imported, the module is executed

module search path:

import modules in other directories:

set PHTYONPATH

import and from:

1. only use import:

ex:

import test

test.run()

2. use import and from

ex:

from test import run

run()

now we can reference run() without test

ex:

from test import *

now we can reference any attribute of module test

show module's attribute

ex:

test.__dict__.keys()

reload:

ex:

import test

reload(test)

module packages:

import  dir1.dir2.test

dir1 and dir2 are directories,  the file imported is test.py

dir1 and dir2 must both contain  __init__.py

dir1 must under the directory of python search path

loop

while  ... else...

the else is executed if break is not excuted in the while

ex:

while  x> 1:

          if  x>10

              break

else

        print  x

for ...  else  is the same as while ...  else ...

for applies to list, string , tuple

lambda

ex:

f= lambda x, y: x+y

f(1,2)

--->  3

define class

ex:

class Test:

     def  __init__(self, name):

     self.name=name

      def  hello(self):

             return  "hello"

t= Test("peter")

t.name

---> "peter"

t.hello

---> "hello"

set

a=set('abcd')

b=set('cdef')

a | b

---> set(['a', 'b', 'c', 'd', 'e',  'f'] )

a & b

--->   set( [ 'c', 'd' ] )

a - b

--->  set( [ 'a', 'b' ] )

file methods

open:

ex:

open('test.txt', 'w')

read:

return entire file into string

sorted, type

sorted

ex:

sorted([2,1])

--->  [1,2]

type:

know the object's type

ex:

type("test")

--->  <type , 'str'> 

check type methods:

(1) if type(a) ==type([]):

(2) if type(a)== list:

(3) if  isinstance(a, list):