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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def build(self):
 """Builds the app in the app's environment. Only builds if the build is out-of-date and is non-empty. Builds in 3 stages: requirements, dev requirements, and app. pip is used to install requirements, and setup.py is used to install the app itself. Raises: ValidationError if the app fails to build. """


        if self.exists:
            self._build(
                'requirements',
                self.requirements_last_modified,
                'pip install -U -r %s' % self.requirements_file
            )
            try:
                self._build(
                    'requirements (dev)',
                    self.dev_requirements_last_modified,
                    'pip install -U -r %s' % self.dev_requirements_file
                )
            except Exception as e:
                if 'No such file' not in str(e):
                    raise e
                self.stdout.write(
                    style.yellow('Could not find dev requirements')
                )
            try:
                self._build(
                    'requirements (local)',
                    self.local_requirements_last_modified,
                    'pip install -U -r %s' % self.local_requirements_file
                )
            except Exception as e:
                if 'No such file' not in str(e):
                    raise e
                self.stdout.write(
                    style.yellow('Could not find local requirements')
                )
            self._build(
                'application',
                self.setup_last_modified,
                'python %s develop' % self.setup_file
            )