code: def pin(package, version, checks, marker, resolving, lazy, quiet):
      
      root = get_root()
      package_name = package.lower()
      version = version.lower()
  
      for check_name in sorted(os.listdir(root)):
          pinned_reqs_file = os.path.join(root, check_name, 'requirements.in')
          resolved_reqs_file = os.path.join(root, check_name, 'requirements.txt')
  
          if os.path.isfile(pinned_reqs_file):
              pinned_packages = {package.name: package for package in read_packages(pinned_reqs_file)}
              if package not in pinned_packages and check_name not in checks:
                  continue
  
              if resolving:
                  pre_packages = list(read_packages(resolved_reqs_file))
              else:
                  pre_packages = list(itervalues(pinned_packages))
  
              if not quiet:
                  echo_info('Check `{}`:'.format(check_name))
  
              if version == 'none':
                  del pinned_packages[package_name]
              else:
                  pinned_packages[package_name] = Package(package_name, version, marker)
  
              package_list = sorted(itervalues(pinned_packages))
              write_file_lines(pinned_reqs_file, ('{}\n'.format(package) for package in package_list))
  
              if not quiet:
                  echo_waiting('    Resolving dependencies...')
  
              if resolving:
                  result = resolve_requirements(pinned_reqs_file, resolved_reqs_file, lazy=lazy)
                  if result.code:
                      abort(result.stdout + result.stderr)
  
              if not quiet:
                  post_packages = read_packages(resolved_reqs_file if resolving else pinned_reqs_file)
                  display_package_changes(pre_packages, post_packages, indent='    ')
docs: Pin a dependency for all checks that require it. This can
      also resolve transient dependencies.
  
      Setting the version to `none` will remove the package. You can
      specify an unlimited number of additional checks to apply the
      pin for via arguments.