# AttributeError: module'itk' has no attribute'GradientDifferenceImageToImageMetric'

**URL:** https://discourse.itk.org/t/attributeerror-moduleitk-has-no-attributegradientdifferenceimagetoimagemetric/4617
**Category:** Beginner Questions
**Tags:** registration, python
**Created:** [November 26, 2021, 7:44am UTC](https://discourse.itk.org/t/attributeerror-moduleitk-has-no-attributegradientdifferenceimagetoimagemetric/4617 "2021-11-26T07:44:25Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![seika](https://discourse.itk.org/letter_avatar_proxy/v4/letter/s/a5b964/32.png) [@seika](https://discourse.itk.org/u/seika)
#### Post date: [November 26, 2021, 7:44am UTC](https://discourse.itk.org/t/attributeerror-moduleitk-has-no-attributegradientdifferenceimagetoimagemetric/4617/1 "2021-11-26T07:44:26Z")

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When I use itk’s GradientDifferenceImageToImageMetric in a python environment, the above error occurred.  
Then I did not find the itkGradientDifferenceImageToImageMetricpython.py file in the packages directory.  
Why does this happen, the itk version is 5.1.2 and the python version is 3.8.  
Thank you!

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### Author: ![dzenanz](https://discourse.itk.org/user_avatar/discourse.itk.org/dzenanz/32/1093_2.png) [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [November 26, 2021, 4:22pm UTC](https://discourse.itk.org/t/attributeerror-moduleitk-has-no-attributegradientdifferenceimagetoimagemetric/4617/2 "2021-11-26T16:22:13Z")

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[GradientDifferenceImageToImageMetric](https://github.com/InsightSoftwareConsortium/ITK/blob/971aef211cad336ba75cb2da114fc86e873444e5/Modules/Registration/Common/include/itkGradientDifferenceImageToImageMetric.h) is currently not wrapped. Adding the wrapping specification should not be hard. It should be similar to other wrap specifications for metrics, e.g. [MeanSquaresImageToImageMetric](https://github.com/InsightSoftwareConsortium/ITK/blob/971aef211cad336ba75cb2da114fc86e873444e5/Modules/Registration/Common/wrapping/itkMeanSquaresImageToImageMetric.wrap). Do you mind [submitting a patch](https://github.com/InsightSoftwareConsortium/ITK/blob/master/CONTRIBUTING.md)?

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### Author: ![seika](https://discourse.itk.org/letter_avatar_proxy/v4/letter/s/a5b964/32.png) [@seika](https://discourse.itk.org/u/seika)
#### Post date: [November 29, 2021, 5:49am UTC](https://discourse.itk.org/t/attributeerror-moduleitk-has-no-attributegradientdifferenceimagetoimagemetric/4617/3 "2021-11-29T05:49:13Z")

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Thanks for your reply, I will try to solve it.