code: def _zero_pad(x, pad, axis):
      """Helper for jnp.pad with 0s for single-axis case."""
      pad_widths = [(0, 0)] * len(x.shape)
      pad_widths[axis] = pad  # Padding on axis.
      return jnp.pad(x, pad_widths, mode="constant")
  
imports: import numpy
  from trax import fastmath
  from trax.fastmath import numpy
  from trax.layers import base
  from trax.layers import combinators
  from trax.layers import convolution
  from trax.layers import core
  from trax.layers import initializers
  from trax.layers.assert_shape import assert_shape
  from trax.layers.base import Fn
  from trax.layers.research import sparsity
label_desc: Use image node_id 12 for calling a global function with example usage: _zero_pad(x, pad, axis) and returns: jnp