class_docstr: A stream operator for warming up a given stream.
  
  Parameters
  ----------
  periods : int
      Number of periods to warm up.
code: def forward(self) -> T:
      v = self.inputs[0].value
      if self.count < self.periods:
          self.count += 1
          return np.nan
      return v
  
file_path: tensortrade/tensortrade/feed/api/generic/warmup.py
imports: import numpy
  from tensortrade.feed.core.base import Stream, T
label_desc: Use image node_id 2 for calling the WarmUp obj's underlying member method code with example usage: obj.forward() and returns: v, np