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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 gatk_major_version(self):
 """Retrieve the GATK major version, handling multiple GATK distributions. Has special cases for GATK nightly builds, Appistry releases and GATK prior to 2.3. """

        full_version = self.get_gatk_version()
        # Working with a recent version if using nightlies
        if full_version.startswith("nightly-"):
            return "3.6"
        parts = full_version.split("-")
        if len(parts) == 4:
            appistry_release, version, subversion, githash = parts
        elif len(parts) == 3:
            version, subversion, githash = parts
        elif len(parts) == 2:
            version, subversion = parts
        elif len(parts) == 1:
            version = parts[0]
        # version was not properly implemented in earlier GATKs
        else:
            version = "2.3"
        if version.startswith("v"):
            version = version[1:]
        return version