docstr: Return the default unit for *x* or None.
code: def default_units(x, axis):
      """Return the default unit for *x* or None."""
      if np.iterable(x):
          for thisx in x:
              return thisx.unit
      else:
          return x.unit
  
file_path: matplotlib/galleries/examples/units/evans_test.py
imports: import matplotlib.pyplot
  import numpy
  import matplotlib.ticker
  import matplotlib.units
label_desc: Use image node_id 3 for calling the FooConverter obj's underlying member method code with example usage: obj.default_units(x, axis) and returns: x, thisx