head first python（第二章）–学习笔记

摘要：第二章学习流程图函数转换为模块函数转换为模块后，就可以灵活的使用模块，方便代码分类，避免代码堆积在一个文件上。使用命令打包代码，生成发布包打包后会生成目录和文件发布后会多了目录和文件，这个是发布的生成的包和相关配置文件。

head first python（第二章）--学习流程图

函数转换为模块后，就可以灵活的使用模块，方便代码分类，避免代码堆积在一个文件上。当你写的python代码达到一定数量并且功能开始丰富的时候，就必须要这么做了。而模块会存在python本地副本目录里面，所以需要打包，需要安装模块到副本目录，以便python解释器能够找到模块，然后使用。

python搜索模块的目录位置：（大致需要知道就行了）

python

Python 2.6.6 (r266:84292, Jan 22 2014, 09:37:14) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path
["", "/usr/lib/python26.zip", "/usr/lib/python2.6", "/usr/lib/python2.6/plat-linux2", "/usr/lib/python2.6/lib-tk", "/usr/lib/python2.6/lib-old", "/usr/lib/python2.6/lib-dynload", "/usr/lib/python2.6/site-packages"]
>>> 

创建目录nester

mkdir nester

进入nester目录并创建nester.py 和setup.py

cd netster

vi nester.py

"""This is the "nester.py" module and it provides one function called print_lol() 
    which prints lists that may or may not include nested lists."""

def print_lol(the_list):
    """This function takes one positional argument called "the_list", which 
        is any Python list (of - possibly - nested lists). Each data item in the 
        provided list is (recursively) printed to the screen on it’s own line."""

for each_item in the_list:
    if isinstance(each_item, list):
        print_lol(each_item)
    else:
        print(each_item)

nester.py代码模块文件，格式要严谨，不必加上其他的东西。

vi setup.py

from distutils.core import setup

setup( 
    name         = "nester", 
    version      = "1.0.0", 
    ## TODO: be sure to change these next few lines to match your details!
    py_modules   = ["nester"],
    author       = "hfpython",
    author_email = "hfpython@headfirstlabs.com",
    url          = "http://www.headfirstlabs.com",
    description  = "A simple printer of nested lists",
 )

setup.py是模块发布的元文件metafile，里面包含模块的一些发布信息。按照格式和要求编写即可。

python setup.py sdist
running sdist
warning: sdist: manifest template "MANIFEST.in" does not exist (using default file list)
warning: sdist: standard file not found: should have one of README, README.txt
writing manifest file "MANIFEST"
creating nester-1.0.0
making hard links in nester-1.0.0...
hard linking nester.py -> nester-1.0.0
hard linking setup.py -> nester-1.0.0
creating dist
tar -cf dist/nester-1.0.0.tar nester-1.0.0
gzip -f9 dist/nester-1.0.0.tar
tar -cf dist/nester-1.0.0.tar nester-1.0.0
gzip -f9 dist/nester-1.0.0.tar
removing "nester-1.0.0" (and everything under it)

打包后会生成目录dist和文件MANIFEST

├── dist
│   └── nester-1.0.0.tar.gz
├── MANIFEST
├── nester.py
└── setup.py

cat MANIFEST

nester.py
setup.py

  
发布后会多了dist目录和MANIFEST文件，这2个是发布的生成的包和相关配置文件。

python setup.py install

running install
running build
running build_py
copying nester.py -> build/lib
running install_lib
copying build/lib/nester.py -> /usr/lib/python2.6/site-packages
byte-compiling /usr/lib/python2.6/site-packages/nester.py to nester.pyc
running install_egg_info
Removing /usr/lib/python2.6/site-packages/nester-1.0.0-py2.6.egg-info
Writing /usr/lib/python2.6/site-packages/nester-1.0.0-py2.6.egg-info

安装后

.
├── build
│   └── lib
│   └── nester.py
├── dist
│   └── nester-1.0.0.tar.gz
├── MANIFEST
├── nester.py
└── setup.py

  
安装后悔出现build目录，这个就是用发布包解压出来的库和模块代码，会统一放到python的模块搜索目录里面去。

不过出现了错误

>>> import nester
>>> print_lol(a)
Traceback (most recent call last):
  File "", line 1, in 
NameError: name "print_lol" is not defined
>>> 

  
是因为命名空间的关系,主python程序中（以及idle shell中）的代码与一个名为main的命名空间关联。所以的话不能直接使用print_lol，而要加上命名空间nester.print_lol()

知识点：

1.命名空间是为了让python解释器就会知道去哪里找这个函数，命名空间格式：首先是模块名字，然后是一个点号，再后面是函数名。

2.如果使用from nester import print_lol,就会把指定的函数print_lol增加到当前命名空间中，这样就不用加上命名空间来调用函数了。

这样可以增加功能而不用增加多余函数代码（print_lol2）。

  
写新代码之前先考虑BIF（内置函数）

  
rang() 返回一个迭代器，根据需要生成一个指定范围的数字。

根据需求写了这样的代码，但运行报错
增加了一个level参数，默认等于0，遇到嵌套列表就是用rang（level）来进行缩进

def print_lol(a_list, level=0):
    """Prints each item in a list, recursively descending
    into nested lists (if necessary)."""

for each_item in a_list:
    if isinstance(each_item, list):
        print_lol(each_item, level)
    else:
        for l in range(level):
            print("	", end="")
        print(each_item)

出现错误了：TypeError:print_lol() take exactly 2 positional arguments (1 given)

原因是print_lol需要2个参数，目前只有一个。

要改成

def print_lol(a_list, level=0):
    """Prints each item in a list, recursively descending
    into nested lists (if necessary)."""

for each_item in a_list:
    if isinstance(each_item, list):
        print_lol(each_item, level+1)  #因为不加1的话函数调用还是会出现level=0，就没有意义了
    else:
        for l in range(level):
            print("	", end="")
        print(each_item)

然后更新代码发布包

from distutils.core import setup

setup( 
    name         = "nester", 
    version      = "1.1.0",     #这里改成1.1.0了，更新了新代码版本
    ## TODO: be sure to change these next few lines to match your details!
    py_modules   = ["nester"],
    author       = "hfpython",
    author_email = "hfpython@headfirstlabs.com",
    url          = "http://www.headfirstlabs.com",
    description  = "A simple printer of nested lists",
 )

因为增加了level参数，改变了默认的行为（最原始的默认行为不想要缩进），导致打印出来的格式有异常，需要再增加一个可选参数，来控制缩进功能的使用。

增加一个indent参数来控制缩进是否打开

def print_lol(a_list, indent=False, level=0):
    """Prints each item in a list, recursively descending
    into nested lists (if necessary)."""

for each_item in a_list:
    if isinstance(each_item, list):
        print_lol(each_item, indent, level+1)
    else:
        if indent:
            for l in range(level):
                print("	", end="")
        print(each_item)

  
需要注意的是所有代码如果不是idel中运行的话，都需要加上#!/usr/bin/python在顶部。

原文链接：http://www.godblessyuan.com/2015/04/13/head_first_python_chapter_2_lea...