Head First Python

1 meet python – Everyone loves lists

P20

isinstance(var, type) 判断变量是哪个类型,类型匹配，返回True,否则,False。

>>> names = ['Michael', 'Terry']
>>> isinstance(names, list)
True
>>> num_names = len(names)
>>> isinstance(num_names, list)
False

P21

查看built-in functions (__builtins__),查看帮助文档help(BIF_name)。

>>>a = 1 
>>>dir(a)
['__abs__', '__add__', '__and__', '__class__', '__cmp__', '__coerce__', '__delattr__', '__div__', '__divmod__', '__doc__', '__float__', '__floordiv__', '__format__', '__getattribute__', '__getnewargs__', '__hash__', '__hex__', '__index__', '__init__', '__int__', '__invert__', '__long__', '__lshift__', '__mod__', '__mul__', '__neg__', '__new__', '__nonzero__', '__oct__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdiv__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'conjugate', 'denominator', 'imag', 'numerator', 'real']
>>>a = []
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__delslice__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getslice__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__setslice__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

P31

Python default recursion limit 1000, 可以用sys.getrecursionlimit()查看。如果需要更大，可以修改。

2 sharing your code – Modules of functions

PyPI is short for Python Package Index.

P38

查看Python模块路径，import sys; sys.path,用;可以把多行放在一行中。 or

>>>import sys
>>>sys.path

P40

distribute module:

1. Create a folder and put module files into it.
2. Create a file called setup.py in the new folder, and input the following code.
3. Build a distribution file.python3 setup.py sdist.
4. Install your distribution into your local coypy of Python.sudo spython3 setup.py install.

from distutils.core import setup

setup(
        name            = 'module name',
        version         = '1.0.0',
        py_modules      = ['module name'],
        author          = '',
        author_email    = '',
        url             = '',
        description     = '',
    )

files structure:

nester
|-- MANIFEST
|-- build
|   |-- lib
|   |   |-- nester.py
|-- dist
|   |-- nester-1.0.0.tar.gz
|-- nester.py
|-- nester.pyc
`-- setup.py

P63

def func(argv_1, argv_2=0), argv_2是可选的，func(arg,1)与func(arg)都可以。带默认值的参数要在最后。 if function is like def func(argv_1, argv_2 = 0, argv_3 = 0, argv_4 = 0), you just want set argv_4 a new value and leave the others default, you must call like this func(argv_1_value, argv_4=1).

P71

• BIFs have their own namespaces called __builtins__, and they are alutomatically included in every python program.
• range() returns an iterator.
• print("\t", end=''), including end='' as an argument to print() switches off its automatic inclusion of a new-line on output.

3 files and exceptions – Dealing with errors

P75

open() creates an iterator to feed the lines of data from your file to your code one line at one time.

P77

split() returns a list of strings. See the doc of split with help(s.split).

>>>s = "aaaaa:bbbbb"
>>>(first, second) = s.split(":")
['aaaaa', 'bbbbb']
>>>help(s.split)

P86

Keyword not negates the value, eg if not a== -1

P93

Ignore errors by pass.

4 persistence – Saving data to files

P110

Write things to file.

# if you want to use print to file, you must import the following.
from __future__ import print_function
out = open("data", "w")
print("This is the thing to be written.", file=out)
out.close() #flushing

By default, print() use standard output(usually screen), to write data to a file, using the file argument to specify the file object.

File access mode:

P115

try:
    ...
except :
    ...
finally:
    ...

P118

The locals() BIF returns a collection of names defined in the current scope.

P119

print exception object.

try:
    ...
except IOError as err:
    print("File Error: " + str(err))

P120

The with statement, when used with files, it negates the need to include a finally suite to handle the closing of a potentially opened file. The usual try/except/finally pattern:

try:
    data = open('its.txt', 'w')
    print("it's ...", file=data)
except IOError as err:
    print('File error: ' + str(err))
finally:
    if 'data' in locals():
        data.close()

The use of with negates the need for the finally suite.

try:
    with open('its.txt', 'w') as data:
        print("it's ...", file=data)
except IOError as err:
    print('File error: ' + str(err))

P133

Standard library pickle (support only for Python 3, not rigth!!) can save and load almost any python data object. The file must be opened in b mode.

import pickle
    ...
with open('mydata.pickle', 'wb') as mysavedata:
    pickle.dumb([1, 2, 'three'], mysavedata)
    ...
with open('mydata.pickle', 'rb') as myrestoredata:
    a_list = pickle.load(myrestoredata)

print(a_list)

5 comprehending data – Work that data!

P144

Two kinds of sort. By default, they are in ascending order, pass reverse=True to order in descending.

• In-place sorting. sort(), the original data is lost.
• Copied sorting. sorted(), return a sorted copy, the original data is still there.

P146

• method chaining. data.strip().split(','), read it from left to rigth.
• function chaining. print(sorted(names)).Apply a series of functions to your data, each function takes your data and performs some operation on it, then passes the transformed data onto the next function. read from ** right to left**

P155

List comprehensions. new_data = [item * 2 for item in data].

P166

set data structure, data items in a set are unordered and duplicates are not allowed.

#Factory function is used here
dist = set()
dis = {1, 2, 3, "four", 2} #there will be only one 2
dis = set(jame_list)

6 custom data objects – Bundling code with data

P176

pop(0) returns and removes data from the fornt of a list.

P180

#create a dictionary
>>>a = {}
>>>b = dict()
>>>type(a)
<class, 'dict'>
>>>a['name'] = 'aaaa'
>>>a['name']
'aaaa'

P191

define class:

class Myclass:
    def __init__(self, value=0):
        self.thing = value  #class attribute

a = Myclass() # Myclass().__init__(a)

Every method defined in class requires self as the first argument. self is used to identify the calling of object instance.

P206

Inherit from other class.

class Myclass(list):
    def __init__(self, a_name):
        list.__init__([])
        self.name = a_name

7 web development – Putting it all together

P224

The standard library string module includes a class called Template , which supports simple string substitutions.

P234

webapp
|-- cgi-bin
|-- data
|-- images
|-- templates

P235

The standard library http.server can be used to build a simple web server in python.

from http.server import HTTPServer, CGIHTTPRequestHandler

port = 8080
httpd = HTTPServer(('', port), CGIHTTPRequestHandler)
print("starting simple_httpd in port: " + str(httpd.server_port))
httpd.server_forever()

238

The standard library glob can be used list of filenames.

import glob
files = glob.glob("data/*.txt")

P244

Get the form data

import cgi
form_data = cgi.FieldStorage()
value = form_data['value_name'].value

P248

The standard library cgitb module, when enabled, can show you CGI coding errors in your browser.

import cgitb
cgitb.enable()

P250

@property, a decorator that lets arrange for a class method to appear as if it is a class attribute.

@property
def top1(self):
    return sorted(self.score_list)[0]
#This method can be used like print("top 1 " + str(top1))

8 mobile app development – Small devices

Scripting Layer for Android(SL4A)

P263

Install and configure Android scripting. 1. Open emulator’s or mobile’s browser, surt to (http://code.google/com/p/android-scripting). 2. Download and intsall sl4a_r*.apk. 3. Download and install python_for_android_r*.apk.

P269

The usage of JSON.

>>> import json
>>> alpha = ['aaa', ['bbb', 'ccc'], 'ddd', ['eee', 'fff', 'ggg']]
>>> alpha
['aaa', ['bbb', 'ccc'], 'ddd', ['eee', 'fff', 'ggg']]
>>> 
>>> to_transfer = json.dumps(alpha)
>>> to_transfer
'["aaa", ["bbb", "ccc"], "ddd", ["eee", "fff", "ggg"]]'
>>> 
>>> from_transfer = json.loads(to_transfer)
>>> from_transfer
[u'aaa', [u'bbb', u'ccc'], u'ddd', [u'eee', u'fff', u'ggg']]
>>> alpha
['aaa', ['bbb', 'ccc'], 'ddd', ['eee', 'fff', 'ggg']]

P291

The sys module provides the sys.stdin, sys.stdout, sys.stderr inpurt streams.

9 manage your data – Handling input

### P302 The standard os library includes the environ dictionary providing convenient access to your program’s environment settings.

import os
addr = os.environ['REMOTE_ADDR']
host = os.environ['REMOTE_HOST']

The usage of sqlite3.

10 scaling your webapp – Getting real

This chapter talks about how to build your webapp based on GAE.

11 dealing with complexity – Data wrangling

It’s about reading data from csv file.