win32com中重写Visio Shape属性setter失败问题求助

I've run into this exact issue with win32com and Visio before—here's what's going on and how to fix it:

The Context #

You're using Python's win32com library to control Visio, and you want cleaner syntax for accessing shape sheet values. Your standard approach works fine:

print(shp.CellsU('PinX').ResultStr('')) # Get value
shp.CellsU('PinX').FormulaU = '1' # Set value

But when you tried adding a PinX property to the Shape class to enable shp.PinX (get) and shp.PinX = '1' (set), the getter worked but the setter threw this error:

KeyError Traceback (most recent call last)
~\AppData\Local\conda\conda\envs\YG_Package_1\lib\site-packages\win32com\client\__init__.py in __setattr__(self, attr, value)
 478         try:
---> 479             args, defArgs=self._prop_map_put_[attr]
 480         except KeyError:
KeyError: 'PinX'

During handling of the above exception, another exception occurred:

AttributeError Traceback (most recent call last)
<ipython-input-28-23f68b65624d> in <module>()
----> 1 shp.PinX= '1'

~\AppData\Local\conda\conda\envs\YG_Package_1\lib\site-packages\win32com\client\__init__.py in __setattr__(self, attr, value)
 479             args, defArgs=self._prop_map_put_[attr]
 480         except KeyError:
---> 481             raise AttributeError("'%s' object has no attribute '%s'" % (repr(self), attr))
 482         self._oleobj_.Invoke(*(args + (value,) + defArgs))
 483 

AttributeError: '<win32com.gen_py.Microsoft Visio 15.0 Type Library.IVShape instance at 0x85710888>' object has no attribute 'PinX'

Why This Happens #

The root issue is how win32com handles attribute assignment for COM proxy objects:

• For getters: The proxy's __getattr__ checks Python class-level properties first, then falls back to COM native properties. That's why your PinX getter worked.
• For setters: The proxy's __setattr__ prioritizes the COM object's native property map (_prop_map_put_) over Python properties. When you try to assign shp.PinX, it looks for a native COM setter (which doesn't exist) and throws the error before ever hitting your Python property setter.

Solutions #

1. Use a Wrapper Class (Recommended) #

This is the most reliable approach, as it avoids messing with win32com's internal logic. We'll create a wrapper that delegates most functionality to the original shape but adds our custom properties:

class VisioShapeWrapper:
    def __init__(self, shape):
        self.shape = shape
    
    @property
    def PinX(self):
        return self.shape.CellsU('PinX').ResultStr('')
    
    @PinX.setter
    def PinX(self, value):
        self.shape.CellsU('PinX').FormulaU = value
    
    # Add more properties like PinY, Width, Height here as needed
    
    # Delegate other attributes/methods to the original shape
    def __getattr__(self, attr):
        return getattr(self.shape, attr)
    
    def __setattr__(self, attr, value):
        # Handle our custom properties first
        if attr in ['PinX', 'PinY']:  # Add your custom props to this list
            object.__setattr__(self, attr, value)
        elif attr == 'shape':
            object.__setattr__(self, attr, value)
        else:
            # Pass through to the original shape for all other attributes
            setattr(self.shape, attr, value)

Usage:

# Wrap your existing shape object
shp_wrapper = VisioShapeWrapper(shp)

# Now use the clean syntax
print(shp_wrapper.PinX)  # Returns the correct value
shp_wrapper.PinX = '2'   # Sets the value successfully
# You can still access all native shape features
shp_wrapper.Name = "Updated Shape Name"

2. Monkey-Patch the Shape Class (Quick Scripts Only) #

If you want to modify the original class directly (not ideal for large projects), override the __setattr__ method to check for your custom properties first:

ShapeClass = type(shp)
original_setattr = ShapeClass.__setattr__

def custom_setattr(self, attr, value):
    # Handle our custom properties
    if attr == 'PinX':
        self.CellsU('PinX').FormulaU = value
    elif attr == 'PinY':
        self.CellsU('PinY').FormulaU = value
    # Add other custom properties here
    else:
        # Fall back to the original setter for native attributes
        original_setattr(self, attr, value)

# Override the class's __setattr__
ShapeClass.__setattr__ = custom_setattr

# Add the getter property as before
def GetPinX(self):
    return self.CellsU('PinX').ResultStr('')
ShapeClass.PinX = property(GetPinX)

Usage:

print(shp.PinX)  # Works as before
shp.PinX = '1'   # Now works without errors!

内容的提问来源于stack exchange，提问作者y4cine