C++博客-I believe-随笔分类-Python

Python extract all comments:提取所有comments,提取c/c++中注释Python脚本

luis — Mon, 03 Dec 2012 00:35:00 GMT

注意，我们只是简单的提取// 以及/* */之间的内容。
如果程序中出现了“/*”,会有bug

#!/usr/bin/env python

import sys
import re

def comment_finder(text):
    pattern = re.compile( r'//.*?$|/\*.*?\*/', re.DOTALL | re.MULTILINE)
    result = pattern.findall(text)
    return result

def print_command(filename):

    codefile = open(filename,'r')
    commentfile = open(filename+".txt",'w')
    lines=codefile.read()
    codefile.close()
    #the list of comments
    list_of_comments = comment_finder(lines)
    for comment in list_of_comments:
        #print comment[0:2]
        if comment[0:2] == "//":
                comment_to_write = comment[2:]
        else:
            comment_to_write = comment[2:-2]
        if len(comment_to_write)!=0:
            commentfile.write(comment_to_write)
        commentfile.write('\n')
    commentfile.close()

if __name__ == "__main__":
    for filename in sys.argv[1:]:
        print_command(filename)

使用：

在linux下面转到当前目录 ./get_comment.py *
或者指定文件类型

./get_comment.py *.c

luis 2012-12-03 08:35 发表评论

Python 笔记 pi tan 等公式

luis — Thu, 08 Nov 2012 00:21:00 GMT

import math
def mianji(n,s):

temp=1/4*n*(s**2)/math.tan(math.pi/n)

return temp

print mianji(5,7)
============
使用时math.pi math.tan

luis 2012-11-08 08:21 发表评论

Python 笔记2 //

luis — Wed, 07 Nov 2012 22:43:00 GMT

Python “” ‘’ 都可以表示字符串

s1 = "hello,world"
如果要写成多行，那么就要使用/ (“连行符”)吧，如
s2 = "hello,/
world"
s2与s1是一样的。如果你用3个双引号的话，就可以直接写了，如下：
s3 = """hello,
world,
hahaha."""，那么s3实际上就是"hello,/nworld,/nhahaha.", 注意“/n”

s5 = "Let's go"
s4 = 'Let/'s go'

我们也可以把''' ''' 作为多行注释

str(object) 可以将所有转化为字符串。

python	java	描述
or	\|\|	逻辑或
and	&&	逻辑与
not	！	逻辑非
<，>，<=，>=，==，!=或<>	<，>，<=，>=，==，!=	比较操作
is，is not	instanceof	身份认证
\|	\|	位或
&	&	位与
^	^	位异或
<<，>>	<<，>>	移位
+，-，*，/	+，-，*，/	加减乘除
%	%	余数
~	~	位取补

//运算符
10/3==3
120//10==12
121//10==12
122//10==12
130//10==13
10//3.0==3.0

A new operator, //, is the floor division operator. (Yes, we know it
looks like C++'s comment symbol.) // always performs floor division no
matter what the types of its operands are, so 1 // 2 is 0 and 1.0 //
2.0 is also 0.0.

not ()

luis 2012-11-08 06:43 发表评论

label switching

luis — Tue, 30 Oct 2012 19:36:00 GMT

label switching:
比如有两箱苹果：第一个箱子内有两个苹果，label 为a 的概率为30%,为b的概率70%，第二个箱子内有四个苹果，label为b的概率40%,label 为a的概率60%.
如果我们求所有的苹果的重量，只需要将所有的箱子内的苹果取出来求重量即刻。
但是我们先求label a的箱子苹果的重量，加上label b的箱子苹果的重量，可能出现两次取的是同一个箱子，这就是label switching问题。

luis 2012-10-31 03:36 发表评论

Python generate corpus using Dirichlet distribution

luis — Sun, 28 Oct 2012 02:13:00 GMT

At first, let's define the sample function:

def sample(dist, num_samples=1):
    """
    Uses the inverse CDF method to return samples drawn from an
    (unnormalized) discrete distribution.

    Arguments:

    dist -- (unnormalized) distribution

    Keyword arguments:

    num_samples -- number of samples to draw
    """

    cdf = cumsum(dist)
    r = uniform(size=num_samples) * cdf[-1]

    return cdf.searchsorted(r)

As we can see, the sample function input two parameters, one is dist, which can be an un-normalized distribution, another is the sample we want to draw.

Let's see how to generate corpus for Dirichlet--multinomial unigram language model

def generate_corpus(beta, mean, N):
    """
    Returns a corpus of tokens drawn from a Dirichlet--multinomial
    unigram language model. Each token is an instance of one of V
    unique word types, represented by indices 0, , V - 1.

    Arguments:

    beta -- concentration parameter for the Dirichlet prior
    mean -- V-dimensional mean of the Dirichlet prior
    N -- number of tokens to generate
    """

    pass # YOUR CODE GOES HERE
    #print mean
    #print beta
    #print dot(mean,beta)
    #print dirichlet(mean*beta,size=1)
    temp=sample(dirichlet(beta*array(mean),size=1),N)
    #print temp
    return temp

please keep in mind the dirichlet function is “from numpy.random.mtrand import dirichlet"
and the parameters it receives are corresponding to beta*array(mean). beta is the concentration factor, and mean is the vector which sum to 1.

another way is to generate corpus is using the property:
P(D'|D,H)= Nv+beta_nv/N+beta

def generate_corpus_collapsed(beta, mean, N):
    """
    Returns a corpus of tokens drawn from a Dirichlet--multinomial
    unigram language model using the 'collapsed' generative process
    (i.e., phi is not explicitly represented). Each token is an
    instance of one of V unique word types.

    Arguments:

    beta -- concentration parameter for the Dirichlet prior
    mean -- V-dimensional mean of the Dirichlet prior
    N -- number of tokens to generate
    """

    V = len(mean) # vocabulary size

    corpus = zeros(N, dtype=int) # corpus

    Nv = zeros(V, dtype=int) # counts for each word type

    pass # YOUR CODE GOES HERE
    for n in xrange(N):
        corpus[n]=sample((Nv+beta*array(mean))/(n+beta),1)
        Nv[corpus[n]]+=1;
    return corpus

Let's see how to generate corpus for Mixture of Dirichlet-multinomial unigram language model

def generate_corpus(alpha, m, beta, n, D, Nd):
    """
    Returns a grouped corpus drawn from a mixture of
    Dirichlet--multinomial unigram language models.

    Arguments:

    alpha -- concentration parameter for the Dirichlet prior over theta
    m -- T-dimensional mean of the Dirichlet prior over theta
    beta -- concentration parameter for the Dirichlet prior over phis
    n -- V-dimensional mean of the Dirichlet prior over phis
    D -- number of documents to generate
    Nd -- number of tokens to generate per document
    """
    corpus = GroupedCorpus()

    pass # YOUR CODE GOES HERE
    #determine the topic the distribution for topic dirichlet(dot(m,alpha),size=1)
    #given the topic, the distribtuion for word dirichlet(dot(n,beta),size=1)
    theta=dirichlet(alpha*array(m),1)
    phis=dirichlet(beta*array(n),len(m))
    for d in range(0,D):
        [t]=sample(theta,1)
        #print groupVcab
        corpus.add(str(d),str(t),[str(x) for x in sample(phis[t,:],Nd)])
    return corpus

注意是T个topic (group)， phis=dirichlet(beta*array(n),len(m)) 产生了T个 dirichlet distribution,相同的topic t应该取同一个 dirichlet distribution phis[t,:]

luis 2012-10-28 10:13 发表评论

Python 空数组

luis — Wed, 19 Sep 2012 01:47:00 GMT

Python array 用法
直接 result=[]

for x in range(0,N):

temp=beta(b,n)

print temp

if temp >= n:

result.append("Yes") #直接append

else:

result.append("No") #直接append

return result

luis 2012-09-19 09:47 发表评论

Python笔记

luis — Sun, 09 Sep 2012 06:47:00 GMT

Tutorial ： http://www.tutorialspoint.com/python/python_files_io.htm

Python IO
输出 print

str = raw_input("Enter your input: "); print "Received input is : ", str

Python只有三种变量类型 int, string, float?
typeof(1.5)
貌似不支持隐式类型转换
print str(2.5) 对
print 2.5 错
print '2.5' 对

python 定义方法是
def MethodName(para,para2): #注意这里的冒号
if

python注释
#单行注释
""" 三个双引号是多行注释 """

python 引用
include math

Python的str
str(var)类型转换
len(var)
var.upper()
var.lower()
var[2] 第三个（注意下标从0开始）元素，类似于list
var[:3] 前三个元素，实际上指的是0截止到3-1的元素
var[2:4]下标是2到4-1的所有元素

Python的list
exampe=[a,b,c,d,e,f];
len(exampe)
自带sort方法

Python的dictionary
key -value对应
value可以是一个list
注意方括号[]里面只能使用key
区分 del dict['Name']

del dict['Name']; # remove entry with key 'Name' dict.clear();     # remove all entries in dict del dict ;        # delete entire dictionary

自带的方法：

1	cmp(dict1, dict2) Compares elements of both dict.
2	len(dict) Gives the total length of the dictionary. This would be equal to the number of items in the dictionary.
3	str(dict) Produces a printable string representation of a dictionary
4	type(variable) Returns the type of the passed variable. If passed variable is dictionary then it would return a dictionary type.

Python类的定义和类方法的定义
定义类不需要用def class,直接

class ClassName(object):
每个类都有 __init__(self,arg):
方法，注意是左右各两个下划线，总共4根下划线

类方法都需要包含self这个参数，但是使用的时候不需要self,见下例

例如

class Adder(object):

def __init__(self):

self.baseNum = 2

def prnt_num(self):

print self.baseNum

def add_to_base(self, arg):

# Your code here

self.baseNum+=arg

print self.baseNum

objectVar = Adder()

objectVar.prnt_num()

# Your code here

objectVar.add_to_base(3)

Python中的类变量不能 self.xxx来引用，但是成员变量可以
Class variables are special because they belong to the class; the objects created do not get their own copies of the class variable. Class variables are accessed using the class name and dot notation.
ClassName.classVar
Class variables are created outside of__init__
例如：

class Widget(object):

objID = 0

def __init__(self):

Widget.objID += 1

# Your code here

self.myID=Widget.objID

常犯错误：indentation is very important
python indentation error expected an indented block
还有一个错误就是类方法，必须使用 self参数，即使没有参数！！
另外一个常错的地方就是 __init__(self,arg) 一定是四根下划线

不仅要记得留dent 还要记得缩进

luis 2012-09-09 14:47 发表评论