What changed wwith Python in WDL change from draft 2 to version 1?
Complements of Phil Shapiro;
Use ~{} instead of ${}.
So this example from the current docs is wrong:
task heredoc {
  input {
    File in
  }

  command&lt;&lt;&lt;
  python &lt;&lt;CODE
    with open(&quot;${in}&quot;) as fp:
      for line in fp:
        if not line.startswith('#'):
          print(line.strip())
  CODE
  &gt;&gt;&gt;
}

It should be :
task heredoc {
  input {
    File in
  }

  command&lt;&lt;&lt;
  python &lt;&lt;CODE
    with open(&quot;~{in}&quot;) as fp:
      for line in fp:
        if not line.startswith('#'):
          print(line.strip())
  CODE
  &gt;&gt;&gt;
}