在不牺牲内部精度的情况下，限制pyQT QLineEdit中显示的浮点数

Question

我在应用程序中使用QLineEdit小部件来输入和编辑数值（float）值。我希望显示浮点值的四舍五入版本，同时保持完整的内部精度。只有在编辑QLineEdit字段时，才应显示完整的位数。在

有三个原因需要这样做：

• 对于我的GUI来说，复杂的值需要太多的空间

• 用户界面允许在日志和线性表示之间进行选择，我想隐藏由此产生的数值误差。

• 简单地舍入QLineEdit中包含和显示的值不是一个选项，因为我在编辑显示的值时会失去准确性

有人知道解决这个问题的好办法吗？在

下面是一个MWE，完整的代码（pyfda）使用小部件的动态实例化和其他难看的东西。在

# -*- coding: utf-8 -*-
from __future__ import print_function, division
import numpy as np
import sys
from PyQt4 import QtGui

class InputNumFields(QtGui.QWidget):

    def __init__(self, parent):
        super(InputNumFields, self).__init__(parent)
        self.edit_input_float = 10*np.log10(np.pi) # store in log format
        self._init_UI()

    def _init_UI(self):    
        self.edit_input = QtGui.QLineEdit()
        self.edit_input.editingFinished.connect(self.store_entries)
        self.lay_g_main = QtGui.QGridLayout()
        self.lay_g_main.addWidget(self.edit_input, 0, 0)
        self.setLayout(self.lay_g_main)
        self.get_entries()

    def store_entries(self):
        """ Store text entry as log float"""
        self.edit_input_float = 10*np.log10(float(self.edit_input.text()))
        self.get_entries()

    def get_entries(self):
        """ Retrieve float value, delog and convert to string """
        self.edit_input.setText(str(10**(self.edit_input_float/10)))

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    mainw = InputNumFields(None)
    app.setActiveWindow(mainw) 
    mainw.show()
    sys.exit(app.exec_())

Answer 1

我试图混合使用信号槽连接（editingFinished）和eventFilter。但是，我遇到了一些奇怪的bug，这些bug可能是由一些竞争条件引起的，或者仅仅是因为代码背后的逻辑变得过于扭曲。不管怎样，下面的片段很好用，也许对某些人有帮助：

def eventFilter(self, source, event):
    """
    Filter all events generated by the QLineEdit widgets. Source and type
    of all events generated by monitored objects are passed to this eventFilter,
    evaluated and passed on to the next hierarchy level.

    - When a QLineEdit widget gains input focus (QEvent.FocusIn`), display
      the stored value with full precision
    - When a key is pressed inside the text field, set the `spec_edited` flag
      to True.
    - When a QLineEdit widget loses input focus (QEvent.FocusOut`), store
      current value in linear format with full precision (only if
      `spec_edited`== True) and display the stored value in selected format
    """
    if isinstance(source, QtGui.QLineEdit): # could be extended for other widgets
        if event.type() == QEvent.FocusIn:
            self.spec_edited = False
            self.get_entries()
        elif event.type() == QEvent.KeyPress:
            self.spec_edited = True
        elif event.type() == QEvent.FocusOut:
            self._store_entries(source)
    # Call base class method to continue normal event processing:
    return super(InputAmpSpecs, self).eventFilter(source, event)