github.com/google/grumpy@v0.0.0-20171122020858-3ec87959189c/third_party/stdlib/fpformat.py (about)

     1  """General floating point formatting functions.
     2  
     3  Functions:
     4  fix(x, digits_behind)
     5  sci(x, digits_behind)
     6  
     7  Each takes a number or a string and a number of digits as arguments.
     8  
     9  Parameters:
    10  x:             number to be formatted; or a string resembling a number
    11  digits_behind: number of digits behind the decimal point
    12  """
    13  from warnings import warnpy3k
    14  warnpy3k("the fpformat module has been removed in Python 3.0", stacklevel=2)
    15  del warnpy3k
    16  
    17  import re
    18  
    19  __all__ = ["fix","sci","NotANumber"]
    20  
    21  # Compiled regular expression to "decode" a number
    22  decoder = re.compile(r'^([-+]?)0*(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$')
    23  # \0 the whole thing
    24  # \1 leading sign or empty
    25  # \2 digits left of decimal point
    26  # \3 fraction (empty or begins with point)
    27  # \4 exponent part (empty or begins with 'e' or 'E')
    28  
    29  try:
    30      class NotANumber(ValueError):
    31          pass
    32  except TypeError:
    33      NotANumber = 'fpformat.NotANumber'
    34  
    35  def extract(s):
    36      """Return (sign, intpart, fraction, expo) or raise an exception:
    37      sign is '+' or '-'
    38      intpart is 0 or more digits beginning with a nonzero
    39      fraction is 0 or more digits
    40      expo is an integer"""
    41      res = decoder.match(s)
    42      if res is None: raise NotANumber, s
    43      sign, intpart, fraction, exppart = res.group(1,2,3,4)
    44      if sign == '+': sign = ''
    45      if fraction: fraction = fraction[1:]
    46      if exppart: expo = int(exppart[1:])
    47      else: expo = 0
    48      return sign, intpart, fraction, expo
    49  
    50  def unexpo(intpart, fraction, expo):
    51      """Remove the exponent by changing intpart and fraction."""
    52      if expo > 0: # Move the point left
    53          f = len(fraction)
    54          intpart, fraction = intpart + fraction[:expo], fraction[expo:]
    55          if expo > f:
    56              intpart = intpart + '0'*(expo-f)
    57      elif expo < 0: # Move the point right
    58          i = len(intpart)
    59          intpart, fraction = intpart[:expo], intpart[expo:] + fraction
    60          if expo < -i:
    61              fraction = '0'*(-expo-i) + fraction
    62      return intpart, fraction
    63  
    64  def roundfrac(intpart, fraction, digs):
    65      """Round or extend the fraction to size digs."""
    66      f = len(fraction)
    67      if f <= digs:
    68          return intpart, fraction + '0'*(digs-f)
    69      i = len(intpart)
    70      if i+digs < 0:
    71          return '0'*-digs, ''
    72      total = intpart + fraction
    73      nextdigit = total[i+digs]
    74      if nextdigit >= '5': # Hard case: increment last digit, may have carry!
    75          n = i + digs - 1
    76          while n >= 0:
    77              if total[n] != '9': break
    78              n = n-1
    79          else:
    80              total = '0' + total
    81              i = i+1
    82              n = 0
    83          total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1)
    84          intpart, fraction = total[:i], total[i:]
    85      if digs >= 0:
    86          return intpart, fraction[:digs]
    87      else:
    88          return intpart[:digs] + '0'*-digs, ''
    89  
    90  def fix(x, digs):
    91      """Format x as [-]ddd.ddd with 'digs' digits after the point
    92      and at least one digit before.
    93      If digs <= 0, the point is suppressed."""
    94      if type(x) != type(''): x = repr(x)
    95      try:
    96          sign, intpart, fraction, expo = extract(x)
    97      except NotANumber:
    98          return x
    99      intpart, fraction = unexpo(intpart, fraction, expo)
   100      intpart, fraction = roundfrac(intpart, fraction, digs)
   101      while intpart and intpart[0] == '0': intpart = intpart[1:]
   102      if intpart == '': intpart = '0'
   103      if digs > 0: return sign + intpart + '.' + fraction
   104      else: return sign + intpart
   105  
   106  def sci(x, digs):
   107      """Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point
   108      and exactly one digit before.
   109      If digs is <= 0, one digit is kept and the point is suppressed."""
   110      if type(x) != type(''): x = repr(x)
   111      sign, intpart, fraction, expo = extract(x)
   112      if not intpart:
   113          while fraction and fraction[0] == '0':
   114              fraction = fraction[1:]
   115              expo = expo - 1
   116          if fraction:
   117              intpart, fraction = fraction[0], fraction[1:]
   118              expo = expo - 1
   119          else:
   120              intpart = '0'
   121      else:
   122          expo = expo + len(intpart) - 1
   123          intpart, fraction = intpart[0], intpart[1:] + fraction
   124      digs = max(0, digs)
   125      intpart, fraction = roundfrac(intpart, fraction, digs)
   126      if len(intpart) > 1:
   127          intpart, fraction, expo = \
   128              intpart[0], intpart[1:] + fraction[:-1], \
   129              expo + len(intpart) - 1
   130      s = sign + intpart
   131      if digs > 0: s = s + '.' + fraction
   132      e = repr(abs(expo))
   133      e = '0'*(3-len(e)) + e
   134      if expo < 0: e = '-' + e
   135      else: e = '+' + e
   136      return s + 'e' + e
   137  
   138  def test():
   139      """Interactive test run."""
   140      try:
   141          while 1:
   142              x, digs = input('Enter (x, digs): ')
   143              print x, fix(x, digs), sci(x, digs)
   144      except (EOFError, KeyboardInterrupt):
   145          pass