... method chains.

Method chains are an amazing programming pattern if you're building an API that needs to be expressive in how it changes data. In this series of video's we will make a pandas-like datacontainer for lists of dictionaries.


This is the class that we have now.

class Clumper:
    def __init__(self, blob):
        self.blob = blob 

    def keep(self, *funcs):
        data = self.blob 
        for func in funcs:
            data = [d for d in data if func(d)]
        return Clumper(data)

    def head(self, n):
        return Clumper([self.blob[i] for i in range(n)])

    def tail(self, n):
        return Clumper([self.blob[-i] for i in range(1, n+1)])

    def select(self, *keys):
        return Clumper([{k: d[k] for k in keys} for d in self.blob])

    def mutate(self, **kwargs):
      data = self.blob 
      for key, func in kwargs.items():
          for i in range(len(data)):
              data[i][key] = func(data[i])
      return Clumper(data)

We can now perform commands like;

  .keep(lambda d: 'Grass' in d['type'],
        lambda d: d['hp'] < 60)
  .select('name', 'hp')
  .mutate(hp = lambda d: d['hp'] * 2,
          hp4 = lambda d: d['hp'] * 4)

Again, notice how flexible we now are because we can chain these commands together.

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