PyQt的QTextStream類對文本的讀寫簡要說明

本文是關於python的QTextStream類讀寫文本簡要說明。
QTextStream與QDataStream不同的時，前者是處理文本，後者二進制文件。因而QTextStream特別注意文本格式編碼的問題，讀取編碼和寫出編碼方式如果存在不同，則會造成相關數據的誤讀。
以下例子爲創建一個類型結構Movie，然後將此類型通過QTextStream類保存到指定的文本文件，然後從文本文件將保存的內容讀出，讀寫過程類似於Python標準庫對普通的文件操作，但是此方式更加快捷，在開發PyQt Gui程序中，需要保存爲文本格式，這個方法可以借用，但是注意不是所有的pyqt類型直接不經處理寫入文本，畢竟還是要遵循文本的處理規則。文本文件的編碼爲UTF-8，文本的內容格式如下：
{{MOVIE}} God save world
1989 45 2017-01-14
{NOTES}
HELLO WORLD
{{ENDMOVIE}}

from PyQt5.QtCore import  QFile, QFileInfo, QIODevice,QTextStream
import datetime
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 saveQTextStream(self):
        error = None
        fh = None
        try:
            fh = QFile(self.__fname)
            if not fh.open(QIODevice.WriteOnly):
                raise IOError(str(fh.errorString()))
            stream = QTextStream(fh)
            stream.setCodec(CODEC)
            stream << "{{MOVIE}} " << movie.title << "\n" \
                   << movie.year << " " << movie.minutes << " " \
                   << str(movie.acquired) \
                   << "\n{NOTES}"
            if movie.notes:
                stream << "\n" << movie.notes
            stream << "\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(
                    QFileInfo(self.__fname).fileName()))


    def loadQTextStream(self):
        error = None
        fh = None
        try:
            fh = QFile(self.__fname)
            if not fh.open(QIODevice.ReadOnly):
                raise IOError(str(fh.errorString()))
            stream = QTextStream(fh)
            stream.setCodec(CODEC)
            lino = 0
            while not stream.atEnd():
                title = year = minutes = acquired = notes = None
                line = stream.readLine()
                lino += 1
                if not line.startswith("{{MOVIE}}"):
                    raise ValueError("no movie record found")
                else:
                    title = line[len("{{MOVIE}}"):].strip()
                    print(title)
                if stream.atEnd():
                    raise ValueError("premature end of file")
                line = stream.readLine()
                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)
                if stream.atEnd():
                    raise ValueError("premature end of file")
                line = stream.readLine()
                lino += 1
                if line != "{NOTES}":
                    raise ValueError("notes expected")
                notes = ""
                while not stream.atEnd():
                    line = stream.readLine()
                    lino += 1
                    if line == "{{ENDMOVIE}}":
                        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 + "\n"
                        print(notes)
                else:
                    raise ValueError("missing endmovie marker")
        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(
                    QFileInfo(self.__fname).fileName()))

if __name__ == "__main__":

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

運行結果：
Saved 1 movie records to movie.datetxt
God save world
1989
45
2017-01-14
HELLO WORLD

Loaded 1 movie records from movie.datetxt