title: AttributeError: module 're' has no attribute 'IGNORECASE' ...only in pyenv build
body: <p>On my Mac OSX pyenv python 3.7.3, a simple base converter fails with</p>
  
  <pre><code>  File "/Users/geo/.pyenv/versions/3.7.3/lib/python3.7/string.py", line 88, in Template
      flags = _re.IGNORECASE
  </code></pre>
  
  <p>the same code works with brew 3.7.3</p>
  
  <p>reinstalled pyenv 3.7.3, and compared 3.7.3/lib/python3.7/string.py files (they are the same), here is the program</p>
  
  <pre><code>import sys
  import string
  
  digs = string.digits + string.ascii_letters
  
  def d2b(x, b):
      if x &lt; 0:
          sign = -1
      elif x == 0:
          return digs[0]
      else:
          sign = 1
      x *= sign
      digits = []
      while x:
          digits.append(digs[int(x % b)])
          x = int(x / b)
      if sign &lt; 0:
          digits.append('-')
      digits.reverse()
      return ''.join(digits)
  
  print(d2b(int(sys.argv[1]),int(sys.argv[2])))
  </code></pre>
  
  <p>Here is a success, and failed invocation...</p>
  
  <pre><code> /usr/local/bin/python3 lang/py/d2b.py 17 16
  11
   /Users/geo/.pyenv/versions/3.7.3/bin/python3.7 lang/py/d2b.py 17 16
  0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,Traceback (most recent call last):
    File "lang/py/d2b.py", line 3, in &lt;module&gt;
      import string
    File "/Users/geo/.pyenv/versions/3.7.3/lib/python3.7/string.py", line 78, in &lt;module&gt;
      class Template(metaclass=_TemplateMetaclass):
    File "/Users/geo/.pyenv/versions/3.7.3/lib/python3.7/string.py", line 88, in Template
      flags = _re.IGNORECASE
  AttributeError: module 're' has no attribute 'IGNORECASE'
  </code></pre>
  
  <p>Thanks for any tips on where to look next!</p>