17 Aug 2015
模块就是python程序
官方解释：
If you quit from the Python interpreter and enter it again, the definitions you have made (functions and variables) are lost. Therefore, if you want to write a somewhat longer program, you are better off using a text editor to prepare the input for the interpreter and running it with that file as input instead. This is known as creating a script. As your program gets longer, you may want to split it into several files for easier maintenance. You may also want to use a handy function that you've written in several programs without copying its definition into each program. To support this, Python has a way to put definitions in a file and use them in a script or in an interactive instance of the interpreter. Such a file is called a module; definitions from a module can be imported into other modules or into the main module (the collection of variables that you have access to in a script executed at the top level and in calculator mode). A module is a file containing Python definitions and statements. The file name is the module name with the suffix .py appended. Within a module, the module's name (as a string) is available as the value of the global variable __name__.
import module_name>>> import math >>> math.sqrt(16) 4.0 # 不可以直接使用math中的函数或变量 >>> sqrt(16) Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'sqrt' is not defined
from module_name import function>>> from math import sqrt >>> sqrt(16) 4.0 # 不可以用math.sqrt()的方式 >>> math.sqrt(16) Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'math' is not defined
少用
from module import *，会污染命名空间
# 不要跟内置模块重名 # vi os.py ***************************** def say(): print 'hi' *****************************
python解释器默认会寻找当前目录下的py文件，但会忽略和内置模块重名的文件
>>> import os # 报错是因为现在的os是builtin的os模块，没有say() >>> os.say() Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'module' object has no attribute 'say'
让我们把此文件换个名字
mv os.py module_test.py
然后再尝试
>>> import module_test >>> module_test.say() hi
built in module --> sys.path（当前目录包含在sys.path中）# 导入sys module，把/root/py加入到python环境变量里 >>> import sys >>> sys.path # sys.path是sys模块中的一个list，用于储存python路径变量 ['', '/usr/lib64/python27.zip', '/usr/lib64/python2.7', '/usr/lib64/python2.7/plat-linux2', '/usr/lib64/python2.7/lib-tk', '/usr/lib64/python2.7/lib-old', '/usr/lib64/python2.7/lib-dynload', '/usr/lib64/python2.7/site-packages', '/usr/lib/python2.7/site-packages'] >>> sys.path.append("/root/py") >>> sys.path[-1] '/root/py'
# 在python环境变量path中/root/py和当前目录/root中放入统一名称的py文件os.py # 当前目录下的os.py cat /root/os.py def say(): print 'hi,this is /root/ !' # path环境变量/root/py/中的os.py cat /root/py/os.py def say(): print 'hi,this is /root/py !'
进入python解释器验证
>>> import sys >>> sys.path.append("/root/py") >>> import os >>> os.say() Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'module' object has no attribute 'say'
结论1：说明首先调用的是built in的module
接下来我们改掉os.py的名称
mv /root/os.py /root/so.py mv /root/py/os.py /root/py/so.py
重新进入python解释器
>>> import sys >>> sys.path.append("/root/py") >>> import so >>> so.say() hi,this is /root/ !
结论2：说明第二调用的是当前目录的module
删掉当前目录下的py编译文件so.pyc和把当前目录下的so.py改名
mv /root/so.py /root/current_so.py rm -f so.pyc
进入python解释器
>>> import sys >>> sys.path.append("/root/py") >>> import so >>> so.say() hi,this is /root/py !
结论3：由此说明，python调用模块的优先级是bulit in –》 当前目录 –》 sys.path
后来经老师指正：
sys.path[0] = ''，这个''就是当前目录
vi inital.py ****************************** def say(): print 'hi,this is /root/ !' say() ******************************
>>> import inital hi,this is /root/ ! # 初次导入时输出了say() >>> import inital # 再次导入时并未执行say() >>> reload(inital) hi,this is /root/ ! # reload时会再次say() <module 'inital' from 'inital.pyc'> # 模块的导入其实主要是初始化，用于定义一些变量、函数、类等，而且是import only once，如果再次import并不会再次初始化变量等信息
cat inital.py def say(): print 'hi,this is /root/ !' if __name__ == '__main__': say()
进入到python解释器
>>> import inital # 再次导入，不会再输出say()的执行结果了
if __name__ == '__main__':这是用来判断name是不是主函数，如果不是直接执行此模块，此if代码块不会执行
已多次演示，不再赘述
__all__
vi exam1.py ************************************* __all__ = ["print_func"] def print_func(): print "function 1 print() in module" def say(): print "function 2 say() in module" ***************************************
进入python解释器
>>> from exam1 import * >>> say() Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'say' is not defined >>> print_func() function 1 print() in module
重新进入python解释器
>>> import exam1 >>> exam1.say() function 2 say() in module
重新进入python解释器
>>> from exam1 import say >>> say() function 2 say() in module
预留位置
1、答案
chaocai.py
"""we provide the service of make food""" __all__ = ["zuocai", "buy"] def zuocai(cai): print "get your %s, will finish later" % cai qiecai(cai) dianhuo() fanchao(cai) zhuangpan(cai) def buy(cai): print "buy the %s for you, will fire later" %cai zuocai(cai) def qiecai(cai): print "cut %s" % cai def dianhuo(): print "fire is ready" def fanchao(cai): print "stir fry %s for 5 minutes" % cai def zhuangpan(cai): print "transfer %s to a plate" % cai
hungry.py
"""feel hungry? we can make food for you""" from chaocai import * def maicai(cai): print "bought the %s" % cai return cai def ask_to_buy(cai): print "pls buy %s for me" % cai return cai if __name__ == "__main__": if raw_input("do you want buy vege yourself?(yes or no)") == "yes": cai = maicai("cabbage") zuocai(cai) else: cai = ask_to_buy("cabbage") buy(cai)
2、答案
fib_cache.py
'''decorator''' __all__ = ["cache"] def cache(func): cache_dic = dict() def inner(args): if args not in cache_dic: cache_dic[args] = func(args) else: print '\thit cache' return cache_dic[args] return inner
fib.py
'''recurision''' from fib_cache import * @cache def fib(n): if n <= 2: return 1 else: return fib(n-1) + fib(n-2) if __name__ == "__main__": while True: number = raw_input("input a number pls:") if number == 'quit': break try: number = int(number) except ValueError as e: print e print "\t============================\n\tthe %dth fib is %r" %(number, fib(number))