class_docstr: This class represent prefixes, with their name, symbol and factor.
  
  Prefixes are used to create derived units from a given unit. They should
  always be encapsulated into units.
  
  The factor is constructed from a base (default is 10) to some power, and
  it gives the total multiple or fraction. For example the kilometer km
  is constructed from the meter (factor 1) and the kilo (10 to the power 3,
  i.e. 1000). The base can be changed to allow e.g. binary prefixes.
  
  A prefix multiplied by something will always return the product of this
  other object times the factor, except if the other object:
  
  - is a prefix and they can be combined into a new prefix;
  - defines multiplication with prefixes (which is the case for the Unit
    class).
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code: def __str__(self):
      return str(self._abbrev)
  
file_path: sympy/sympy/physics/units/prefixes.py
imports: from sympy.core.expr import Expr
  from sympy.core.sympify import sympify
  from sympy.core.singleton import S
label_desc: Use image node_id 7 for calling the Prefix obj's underlying member method code with example usage: obj.__str__() and returns: str