python codes模块读写文本文件的简要说明

上文是提到关于PyQt的QTextStream类读写文本简要说明。如果利用python标准库编程时，python还提供了用于文本读写的内置类和标准库。使用这些文件类，可以直接读写文件，不过，如果打指定编码方式，就必须使用codes模块。
这个模块对文本的操作与QTextStream非常类似。与QTextStream同样得特别注意文本格式编码的问题，读取编码和写出编码方式如果存在不同，则会造成相关数据的误读。
以下例子为创建一个类型结构Movie，然后将此类型通过codes模块保存到指定的文本文件，然后从文本文件将保存的内容读出，文本文件的编码为UTF-8，文本的内容格式如下：
{{MOVIE}} God save world
1989 45 2017-01-14
{NOTES}
HELLO WORLD
{{ENDMOVIE}}

import codecs
import datetime
import os
CODEC = "UTF-8"
class Movie(object):
    UNKNOWNYEAR = 1890
    UNKNOWNMINUTES = 0
    def __init__(self, title=None, year=UNKNOWNYEAR,
                 minutes=UNKNOWNMINUTES, acquired=None, notes=None):
        self.title = title
        self.year = year
        self.minutes = minutes
        self.acquired = (acquired if acquired is not None
                                  else datetime.date.today())
        self.notes = notes
class MovieContainer(object):

    def __init__(self,fname,movies):
        self.__fname = fname
        self.__movies = movies        

    def saveText(self):
        error = None
        fh = None
        try:
            fh = codecs.open(str(self.__fname), "w", CODEC)
            movie=self.__movies
            fh.write("{{MOVIE}} ")
            fh.write("{0}\n".format(str(movie.title)))
            fh.write("{0} {1} {2}\n".format(movie.year, movie.minutes,
                     movie.acquired))
            fh.write("{NOTES}")
            if movie.notes:
                fh.write("\n{0}".format(str(movie.notes)))
            fh.write("\n{{ENDMOVIE}}\n")
        except EnvironmentError as e:
            error = "Failed to save: {0}".format(e)
        finally:
            if fh is not None:
                fh.close()
            if error is not None:
                print(error)
            print("Saved 1 movie records to {0}".format(
                os.path.basename(self.__fname)))


    def loadText(self):
        error = None
        fh = None
        try:
            fh = codecs.open(str(self.__fname), "rU", CODEC)
            lino = 0
            while True:
                title = year = minutes = acquired = notes = None
                line = fh.readline()
                if not line:
                    break
                lino += 1
                if not line.startswith("{{MOVIE}}"):
                    raise ValueError("no movie record found")
                else:
                    title = line[len("{{MOVIE}}"):].strip()
                    print(title)
                line = fh.readline()
                if not line:
                    raise ValueError("premature end of file")
                lino += 1
                parts = line.split(" ")
                if len(parts) != 3:
                    raise ValueError("invalid numeric data")
                year = int(parts[0])
                minutes = int(parts[1])
                print(year)
                print(minutes)
                ymd = parts[2].split("-")
                if len(ymd) != 3:
                    raise ValueError("invalid acquired date")
                acquired = datetime.date(int(ymd[0]), int(ymd[1]),
                                        int(ymd[2]))
                print(acquired)                
                line = fh.readline()
                if not line:
                    raise ValueError("premature end of file")
                lino += 1
                if line != "{NOTES}\n":
                    raise ValueError("notes expected")
                notes = ""
                while True:
                    line = fh.readline()
                    if not line:
                        raise ValueError("missing endmovie marker")
                    lino += 1
                    if line == "{{ENDMOVIE}}\n":
                        if (title is None or year is None or
                            minutes is None or acquired is None or
                            notes is None):
                            raise ValueError("incomplete record")
                        break
                    else:
                        notes += line
                print(notes)
        except (IOError, OSError, ValueError) as e:
            error = "Failed to load: {0} on line {1}".format(e, lino)
        finally:
            if fh is not None:
                fh.close()
            if error is not None:
                print(error)
            print("Loaded 1 movie records from {0}".format(
                    os.path.basename(self.__fname)) )   
if __name__ == "__main__":

    textdata=[["God save world",1989,45,None,"HELLO WORLD"]]
    fname="/home/yrd/work/movie.codecs"
    for data in textdata:
        movie=Movie(data[0],data[1],data[2],data[3],data[4])
        moviecontainer=MovieContainer(fname, movie)
        moviecontainer.saveText()
        moviecontainer.loadText()

运行结果：
Saved 1 movie records to movie.codecs
God save world
1989
45
2017-01-14
HELLO WORLD

Loaded 1 movie records from movie.codecs