为什么QtNetwork.QFtp.get下载在多个文件的for循环中失败？

Question

我正在尝试使用for-loop从ftp站点下载多个文件。在弹出python.exe关闭窗口之前，下面的代码似乎只适用于循环中的前两个文件。两个下载的文件是完美的，但第三个下载的文件在关机时是空的。我没有得到其余的文件。任何想法可能是什么问题？

from PyQt4 import QtCore, QtGui, QtNetwork 


class FtpWindow(QtGui.QDialog): 

    def __init__(self, parent=None): 
     self.fileList = QtGui.QTreeWidget() 
     self.ftp = QtNetwork.QFtp(self) 
     self.progressDialog = QtGui.QProgressDialog(self) 
     self.downloadAllButton.clicked.connect(self.downloadAllFile) 
     self.ftp.commandFinished.connect(self.ftpCommandFinished) 

    def downloadAllFile(self): 
     for jj in range(self.fileList.topLevelItemCount()): # how many files in a particular folder 
      fileName = self.fileList.topLevelItem(jj).text(0) 
      self.outFile = QtCore.QFile(fileName) 

      self.ftp.get(fileName, self.outFile) #download one file at a time 
      self.progressDialog.setLabelText("Downloading %s..." % fileName)  
      self.progressDialog.exec_() 

    def ftpCommandFinished(self, _, error): 
     self.setCursor(QtCore.Qt.ArrowCursor) 
     if self.ftp.currentCommand() == QtNetwork.QFtp.Get: 
      if error: 
       self.statusLabel.setText("Canceled download of %s." % self.outFile.fileName()) 
       self.outFile.close() 
       self.outFile.remove() 
      else: 
       self.statusLabel.setText("Downloaded %s to current directory." % self.outFile.fileName()) 
       self.outFile.close() 

      self.outFile = None 
      self.enableDownloadButton() 
      self.progressDialog.hide() 

Answer 1

self.progressDialog.exec_()应该是一个阻塞模态对话框。使用self.progressDialog.show()进行非阻塞呼叫。

它看起来像ftp get是非阻塞的，所以你必须等到使用commandFinished（）信号完成下载。

我的猜测是循环中的每个迭代都覆盖self.outFile，因此没有任何对该对象的Python引用。这使得对象在Python执行垃圾回收时死亡。我的猜测是，你的前两个文件小而快，你的第三个文件更大，所以其他文件能够在垃圾回收之前下载。对于最后一个文件，这个或垃圾收集只是更快。

http://pyside.github.io/docs/pyside/PySide/QtNetwork/QFtp.html#PySide.QtNetwork.PySide.QtNetwork.QFtp.get

class FtpWindow(QtGui.QDialog): 

    def __init__(self, parent=None): 
     self.fileList = QtGui.QTreeWidget() 
     self.ftp = QtNetwork.QFtp(self) 
     self.progressDialog = QtGui.QProgressDialog(self) 
     self.progressDialog.canceled.connect(self.ftp.abort) 
     self.downloadAllButton.clicked.connect(self.downloadAllFile) 
     self.ref_holder = {} 
     self.ftp.commandFinished.connect(self.ftpCommandFinished) 

    def download_file(self, filename): 
     """Non blocking start downloading a file.""" 
     outFile = QtCore.QFile(filename) 
     cmd_id = self.ftp.get(filename, outFile) # Non blocking just start downloading 

     # This keeps the object alive and doesn't overwrite them. 
     self.ref_holder[cmd_id] = [filename, outFile] 

    def downloadAllFile(self): 
     self.progressDialog.reset() 
     num_downloads = self.fileList.topLevelItemCount() 
     self.progressDialog.setMaximum(num_downloads) 
     self.progressDialog.setValue(0) 
     self.progressDialog.setLabelText("Downloading %d files ..." % num_downloads) 
     self.progressDialog.show() 
     for jj in range(num_downloads): # how many files in a particular folder 
      fileName = self.fileList.topLevelItem(jj).text(0) 
      self.download_file(fileName) # Non blocking, and doesn't overwrite self.outFile with every iteration 

    def ftpCommandFinished(self, cmd_id, error=None): 
     """Increased the number of items finished.""" 
     self.progressDialog.setValue(self.progressDialog.value()+1) 
     item = self.ref_holder.pop(cmd_id) # Remove the reference for the finished item 
     if error: 
      self.progressDialog.setLabelText("Error downloading %s" % item[0]) 

     # Check if all downloads are done 
     if len(self.ref_holder) == 0: 
      self.progressDialog.setValue(self.progressDialog.maximium()) 
      self.progressDialog.close() # This shouldn't be needed 

我的例子，直到命令完成上述将持有的文件名和不过outFile对象引用。当命令完成时，引用被删除，允许python清理对象。

Answer 2

感谢HashSplat的输入。我有几个更新，使其功能齐全：

class FtpWindow(QtGui.QDialog): 

def __init__(self, parent=None): 
    self.fileList = QtGui.QTreeWidget() 
    self.ftp = QtNetwork.QFtp(self) 
    self.progressDialog = QtGui.QProgressDialog(self) 
    self.progressDialog.canceled.connect(self.ftp.abort) 
    self.downloadAllButton.clicked.connect(self.downloadAllFile) 
    self.ref_holder = {} 
    self.ftp.commandFinished.connect(self.ftpCommandFinished) 

def download_file(self, fileName): 
    """Non blocking start downloading a file.""" 
    self.outFile = QtCore.QFile(fileName) 

    """ Need this to have files saved locally """ 
    if not self.outFile.open(QtCore.QIODevice.WriteOnly): 
     QtGui.QMessageBox.information(self, "FTP", 
       "Unable to save the file %s." % fileName) 
     self.outFile = None 
     return 
    cmd_id = self.ftp.get(filename, self.outFile) # Non blocking just start downloading 

    # This keeps the object alive and doesn't overwrite them. 
    self.ref_holder[cmd_id] = [filename, self.outFile] 

def downloadAllFile(self): 
    self.progressDialog.reset() 
    self.num_downloads = self.fileList.topLevelItemCount() 
    self.counter=1 
    self.progressDialog.setLabelText("Downloading %d/%d files ..." % (self.counter, self.num_downloads)) 
    self.progressDialog.show() 
    for jj in range(num_downloads): # how many files in a particular folder 
     fileName = self.fileList.topLevelItem(jj).text(0) 
     self.download_file(fileName) # Non blocking, and doesn't overwrite self.outFile with every iteration 

def ftpCommandFinished(self, cmd_id, error=None): 
    """Increased the number of items finished.""" 
    self.progressDialog.setValue(self.progressDialog.value()+1) 
    item = self.ref_holder.pop(cmd_id) # Remove the reference for the finished item 
    if error: 
     self.progressDialog.setLabelText("Error downloading %s" % item[0]) 

    # Check if all downloads are done 
    if len(self.ref_holder) == 0: 
     self.progressDialog.close() # This closes the extra window 
     self.outFile.close() # You need this to have the last file saved 
    else: 
     self.counter+=1 
     self.progressDialog.setLabelText("Downloading %d/%d files ..." % (self.counter, self.num_downloads)) 

def updateDataTransferProgress(self, readBytes, totalBytes): 
    self.progressDialog.setMaximum(totalBytes) 
    self.progressDialog.setValue(readBytes)