Dynamically add attributes and generate objects in python classes

This article will solve the problem one by one through the following aspects

1. Main functions of the program

2. Implementation process

3. Class definition

4. Use generator generator to dynamically update each object and return the object

5. Use strip to remove Unnecessary characters

6. rematch the matching string

7. Use timestrptime to extract the string and convert it into a time object

8. Complete code

The main function of the program

Now there is a table-like document that stores user information: the first line is Attributes, each attribute is separated by commas (,). Starting from the second line, each line is the value corresponding to each attribute, and each line represents a user. How to read this document and output one user object per line?
There are also 4 small requirements:

Each document is very large. If so many objects generated by all rows are stored in a list and returned at once, the memory will collapse. Only one line-generated object can be stored in the program at a time.

Each string separated by commas may be preceded or followed by double quotes (") or single quotes ('). For example, "Zhang San", you need to remove the quotes; if it is a number, there are +000000001.24 like this Yes, you need to remove all the + and 0 in front, and extract the time in the 1.24

document. It may be in the form of 2013-10-29, or it may be 2013/10/29 2:23:56. Form, you need to convert such a string into a time type

There are many such documents, each with different attributes. For example, this is the user's information, and that is the call record, so the specifics in the class. Which attributes should be dynamically generated based on the first line of the document

Implementation process

1. Class definition

Since attributes are added dynamically, attribute-value pairs are also added dynamically, and the class must contain two members: updateAttributes() and updatePairs() Function is sufficient. In addition, the list attributes is used to store the attributes, and the dictionary attrilist is used to store the mapping. The init() function is the constructor. An underscore in front indicates a private variable, which cannot be called directly from outside. Just a=UserInfo() is required when instantiating it, without any parameters.

##2. Use a generator to dynamically update each object and return the object

The generator is equivalent to a generator that only needs to be initialized Once, the function can be automatically run multiple times, and each loop returns a result. However, the function uses return to return the result, and the generator uses yield to return the result # each time it is run. ##yield
returns, and the next run starts after

yield

. For example, we implement the Fibonacci sequence using functions and generators: <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>class UserInfo(object): &amp;#39;Class to restore UserInformation&amp;#39; def __init__ (self): self.attrilist={} self.__attributes=[] def updateAttributes(self,attributes): self.__attributes=attributes def updatePairs(self,values): for i in range(len(values)): self.attrilist[self.__attributes[i]]=values[i]</pre><div class="contentsignin">Copy after login</div></div>. We calculate the first 6 numbers of the sequence:

def fib(max):
 n, a, b = 0, 0, 1
 while n < max:
  print(b)
  a, b = b, a + b
  n = n + 1
 return &#39;done&#39;

If you use a generator, just

print

can be changed to

yield

as follows:

##

>>> fib(6)
1
1
2
3
5
8
'done'

Usage:

def fib(max):
 n, a, b = 0, 0, 1
 while n < max:
  yield b
  a, b = b, a + b
  n = n + 1

As you can see, the generator fib itself is an object. Each time it is executed to yield, it will interrupt and return a result. Next time, it will continue to execute from the next line of code in

yield

. The generator can also be executed using

generator.next()

.

In my program, the generator part code is as follows:

>>> f = fib(6)
>>> f
<generator object fib at 0x104feaaa0>
>>> for i in f:
...  print(i)
... 
1
1
2
3
5
8
>>>

Among them, a=UserInfo()

It is an instantiation of class

UserInfo

. Because the document is gb2312 encoded, the corresponding decoding method is used above. Since the first line is attributes, there is a function to store the attribute list in

UserInfo

, that is,

updateAttributes();

The following lines need to read the attribute-value pairs into a dictionary storage. The dictionary in

p.s.python is equivalent to a map.3. Use strip to remove unnecessary charactersFrom the above code, you can see that using

str.strip(somechar)

can remove the somechar characters before and after str. somechar can be a symbol or a regular expression, as above:

def ObjectGenerator(maxlinenum):
 filename='/home/thinkit/Documents/usr_info/USER.csv'
 attributes=[]
 linenum=1
 a=UserInfo()
 file=open(filename)
 while linenum < maxlinenum:
  values=[]
  line=str.decode(file.readline(),&#39;gb2312&#39;)#linecache.getline(filename, linenum,&#39;gb2312&#39;)
  if line==&#39;&#39;:
   print&#39;reading fail! Please check filename!&#39;
   break
  str_list=line.split(&#39;,&#39;)
  for item in str_list:
   item=item.strip()
   item=item.strip(&#39;\"&#39;)
   item=item.strip(&#39;\&#39;&#39;)
   item=item.strip(&#39;+0*&#39;)
   item=catchTime(item)
   if linenum==1:
    attributes.append(item)
   else:
    values.append(item)
  if linenum==1:
   a.updateAttributes(attributes)
  else:
   a.updatePairs(values)
   yield a.attrilist #change to &#39; a &#39; to use
  linenum = linenum +1

##4.re.match Match string

Function syntax:

item=item.strip()#除去字符串前后的所有转义字符，如\t,\n等
item=item.strip('\"')#除去前后的"
item=item.strip('\'')
item=item.strip('+0*')#除去前后的+00...00，*表示0的个数可以任意多，也可以没有

Function parameter description:

Parameters                                                                                                                                                                        .

flags 标志位，用于控制正则表达式的匹配方式，如：是否区分大小写，多行匹配等等。

若匹配成功re.match方法返回一个匹配的对象，否则返回None。`

>>> s='2015-09-18'
>>> matchObj=re.match(r'\d{4}-\d{2}-\d{2}',s, flags= 0)
>>> print matchObj
<_sre.SRE_Match object at 0x7f3525480f38>
1
2
3
4
5

5.使用time.strptime提取字符串转化为时间对象

在time模块中,time.strptime(str,format)可以把str按照format格式转化为时间对象，format中的常用格式有：

%y 两位数的年份表示（00-99）

%Y 四位数的年份表示（000-9999）

%m 月份（01-12）

%d 月内中的一天（0-31）

%H 24小时制小时数（0-23）

%I 12小时制小时数（01-12）

%M 分钟数（00=59）

%S 秒（00-59）

此外，还需要使用re模块，用正则表达式，对字符串进行匹配，看是否是一般时间的格式，如YYYY/MM/DD H:M:S, YYYY-MM-DD等

在上面的代码中，函数catchTime就是判断item是否为时间对象，是的话转化为时间对象。

代码如下：

import time
import re

def catchTime(item):
 # check if it's time
 matchObj=re.match(r'\d{4}-\d{2}-\d{2}',item, flags= 0)
 if matchObj!= None :
  item =time.strptime(item,'%Y-%m-%d')
  #print "returned time: %s " %item
  return item
 else:
  matchObj=re.match(r'\d{4}/\d{2}/\d{2}\s\d+:\d+:\d+',item,flags=0 )
  if matchObj!= None :
   item =time.strptime(item,'%Y/%m/%d %H:%M:%S')
   #print "returned time: %s " %item
  return item

完整代码：

import collections
import time
import re

class UserInfo(object):
 'Class to restore UserInformation'
 def __init__ (self):
  self.attrilist=collections.OrderedDict()# ordered
  self.__attributes=[]
 def updateAttributes(self,attributes):
  self.__attributes=attributes
 def updatePairs(self,values):
  for i in range(len(values)):
   self.attrilist[self.__attributes[i]]=values[i]

def catchTime(item):
 # check if it's time
 matchObj=re.match(r'\d{4}-\d{2}-\d{2}',item, flags= 0)
 if matchObj!= None :
  item =time.strptime(item,'%Y-%m-%d')
  #print "returned time: %s " %item
  return item
 else:
  matchObj=re.match(r'\d{4}/\d{2}/\d{2}\s\d+:\d+:\d+',item,flags=0 )
  if matchObj!= None :
   item =time.strptime(item,'%Y/%m/%d %H:%M:%S')
   #print "returned time: %s " %item
  return item


def ObjectGenerator(maxlinenum):
 filename='/home/thinkit/Documents/usr_info/USER.csv'
 attributes=[]
 linenum=1
 a=UserInfo()
 file=open(filename)
 while linenum < maxlinenum:
  values=[]
  line=str.decode(file.readline(),&#39;gb2312&#39;)#linecache.getline(filename, linenum,&#39;gb2312&#39;)
  if line==&#39;&#39;:
   print&#39;reading fail! Please check filename!&#39;
   break
  str_list=line.split(&#39;,&#39;)
  for item in str_list:
   item=item.strip()
   item=item.strip(&#39;\"&#39;)
   item=item.strip(&#39;\&#39;&#39;)
   item=item.strip(&#39;+0*&#39;)
   item=catchTime(item)
   if linenum==1:
    attributes.append(item)
   else:
    values.append(item)
  if linenum==1:
   a.updateAttributes(attributes)
  else:
   a.updatePairs(values)
   yield a.attrilist #change to &#39; a &#39; to use
  linenum = linenum +1

if __name__ == '__main__':
 for n in ObjectGenerator(10):
  print n  #输出字典，看是否正确

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