如何使 Python 函数成为 return 静态变量？

Question

我正在尝试构建一个 WTForms custom validator 来检查重复的图像哈希。为此，我在我的表单验证器中使用了一个嵌套函数。问题是当我在外部函数中设置一个变量（内部函数的结果）时，任何对外部变量的后续引用都会再次调用内部函数。

例如：

def dupe_check(self, field):
    def get_hash():
        f = field.data
        img = Image.open(f)
        imghash = imagehash.dhash(img)
        f.seek(0)
        return imghash
    imghash = get_hash()
    hashcheck = Sights.query.filter(Sights.image_hash == imghash).first()
    if hashcheck == imghash:
        print('dupe')
        raise ValidationError('duplicate hash!')
    else:
        print('no dupe')

如果运行数据库中没有哈希，我打印 no dupe 并上传图像。

但是，如果哈希存在于数据库中，当执行到 if hashcheck == imghash: 时我崩溃了，因为看起来 imghash 正在再次调用 get_hash() 而不是简单地返回哈希字符串之前设置为 imghash = get_hash()。

您可以在下面看到 imagehash 程序被调用（并崩溃），而不仅仅是哈希字符串。

127.0.0.1 - - [17/Sep/2017 17:49:36] "POST /add HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1997, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1985, in wsgi_app
    response = self.handle_exception(e)
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1540, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/mrrg/dev/flaskimg/project/sights/views.py", line 74, in add_image
    if form.validate_on_submit():
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/flask_wtf/form.py", line 101, in validate_on_submit
    return self.is_submitted() and self.validate()
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/wtforms/form.py", line 310, in validate
    return super(Form, self).validate(extra)
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/wtforms/form.py", line 152, in validate
    if not field.validate(self, extra):
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/wtforms/fields/core.py", line 204, in validate
    stop_validation = self._run_validation_chain(form, chain)
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/wtforms/fields/core.py", line 224, in _run_validation_chain
    validator(form, self)
  File "/home/mrrg/dev/flaskimg/project/sights/forms.py", line 71, in dupe_check
    if hashcheck == imghash:
  File "/home/mrrg/dev/flaskimg/venv/lib/python3.5/site-packages/imagehash/__init__.py", line 85, in __eq__
    return numpy.array_equal(self.hash.flatten(), other.hash.flatten())
AttributeError: 'Sights' object has no attribute 'hash'

我以为imghash = get_hash()会设置一个从内部函数返回的变量的新实例？如何设置一个静态变量来操作，并避免对内部函数的额外调用？

我也尝试在内部函数的 imghash 上设置 global/nonlocal，结果相同。

Answer 1

据我了解，您的代码试图将 Sight 对象与 ImageHash 对象进行比较，但 Sight class 代码实现仅在 2 个 Sight 对象之间进行比较，因此出现错误

如何使 Python 函数成为 return 静态变量？

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