Problem with rospack depends1

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I am new to ROS and using ROS Melodic on Ubuntu 18.04. I was following the tutorials and got stuck with the command rospack depends1 beginner_tutorials

I am getting this message:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/rosdep2/rospack.py", line 59, in init_rospack_interface
    lookup = _get_default_RosdepLookup(Options())
  File "/usr/lib/python2.7/dist-packages/rosdep2/main.py", line 130, in _get_default_RosdepLookup
    verbose=options.verbose)
  File "/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py", line 633, in create_default
    sources = load_cached_sources_list(sources_cache_dir=sources_cache_dir, verbose=verbose)
  File "/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py", line 533, in load_cached_sources_list
    return parse_sources_data(cache_data, origin=cache_index, model=model)
  File "/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py", line 388, in parse_sources_data
    raise InvalidData('line:\n\t%s\n%s' % (line, e), origin=origin)
rosdep2.core.InvalidData: line:
    yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml osx
unsupported pickle protocol: 4
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/rosdep2/rospack.py", line 59, in init_rospack_interface
    lookup = _get_default_RosdepLookup(Options())
  File "/usr/lib/python2.7/dist-packages/rosdep2/main.py", line 130, in _get_default_RosdepLookup
    verbose=options.verbose)
  File "/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py", line 633, in create_default
    sources = load_cached_sources_list(sources_cache_dir=sources_cache_dir, verbose=verbose)
  File "/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py", line 533, in load_cached_sources_list
    return parse_sources_data(cache_data, origin=cache_index, model=model)
  File "/usr/lib/python2.7/dist-packages/rosdep2/sources_list.py", line 388, in parse_sources_data
    raise InvalidData('line:\n\t%s\n%s' % (line, e), origin=origin)
rosdep2.core.InvalidData: line:
    yaml https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml osx
unsupported pickle protocol: 4
[rospack] Error: could not call python function 'rosdep2.rospack.init_rospack_interface'

I have looked at the solutions of the same problem posted earlier, there were two of them but none of their solutions worked for me.