ModuleNotFoundError: No module named 'oemof'

I am getting this kind of error. How to fix it?
 

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ModuleNotFoundError                       Traceback (most recent call last)
<ipython-input-1-3818e4e5ab18> in <module>
      4 
      5 # Default logger of oemof
----> 6 from oemof.tools import logger
      7 from oemof.tools import economics
      8 from oemof import solph