Add fpformat module (#355)

Author: m4ns0ur

Makefile

@@ -97,6 +97,7 @@ STDLIB_TESTS := \
   test/test_colorsys \
   test/test_datetime \
   test/test_dict \
+  test/test_fpformat \
   test/test_list \
   test/test_md5 \
   test/test_mimetools \

third_party/stdlib/fpformat.py

@@ -0,0 +1,145 @@
+"""General floating point formatting functions.
+
+Functions:
+fix(x, digits_behind)
+sci(x, digits_behind)
+
+Each takes a number or a string and a number of digits as arguments.
+
+Parameters:
+x:             number to be formatted; or a string resembling a number
+digits_behind: number of digits behind the decimal point
+"""
+from warnings import warnpy3k
+warnpy3k("the fpformat module has been removed in Python 3.0", stacklevel=2)
+del warnpy3k
+
+import re
+
+__all__ = ["fix","sci","NotANumber"]
+
+# Compiled regular expression to "decode" a number
+decoder = re.compile(r'^([-+]?)0*(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$')
+# \0 the whole thing
+# \1 leading sign or empty
+# \2 digits left of decimal point
+# \3 fraction (empty or begins with point)
+# \4 exponent part (empty or begins with 'e' or 'E')
+
+try:
+    class NotANumber(ValueError):
+        pass
+except TypeError:
+    NotANumber = 'fpformat.NotANumber'
+
+def extract(s):
+    """Return (sign, intpart, fraction, expo) or raise an exception:
+    sign is '+' or '-'
+    intpart is 0 or more digits beginning with a nonzero
+    fraction is 0 or more digits
+    expo is an integer"""
+    res = decoder.match(s)
+    if res is None: raise NotANumber, s
+    sign, intpart, fraction, exppart = res.group(1,2,3,4)
+    if sign == '+': sign = ''
+    if fraction: fraction = fraction[1:]
+    if exppart: expo = int(exppart[1:])
+    else: expo = 0
+    return sign, intpart, fraction, expo
+
+def unexpo(intpart, fraction, expo):
+    """Remove the exponent by changing intpart and fraction."""
+    if expo > 0: # Move the point left
+        f = len(fraction)
+        intpart, fraction = intpart + fraction[:expo], fraction[expo:]
+        if expo > f:
+            intpart = intpart + '0'*(expo-f)
+    elif expo < 0: # Move the point right
+        i = len(intpart)
+        intpart, fraction = intpart[:expo], intpart[expo:] + fraction
+        if expo < -i:
+            fraction = '0'*(-expo-i) + fraction
+    return intpart, fraction
+
+def roundfrac(intpart, fraction, digs):
+    """Round or extend the fraction to size digs."""
+    f = len(fraction)
+    if f <= digs:
+        return intpart, fraction + '0'*(digs-f)
+    i = len(intpart)
+    if i+digs < 0:
+        return '0'*-digs, ''
+    total = intpart + fraction
+    nextdigit = total[i+digs]
+    if nextdigit >= '5': # Hard case: increment last digit, may have carry!
+        n = i + digs - 1
+        while n >= 0:
+            if total[n] != '9': break
+            n = n-1
+        else:
+            total = '0' + total
+            i = i+1
+            n = 0
+        total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1)
+        intpart, fraction = total[:i], total[i:]
+    if digs >= 0:
+        return intpart, fraction[:digs]
+    else:
+        return intpart[:digs] + '0'*-digs, ''
+
+def fix(x, digs):
+    """Format x as [-]ddd.ddd with 'digs' digits after the point
+    and at least one digit before.
+    If digs <= 0, the point is suppressed."""
+    if type(x) != type(''): x = repr(x)
+    try:
+        sign, intpart, fraction, expo = extract(x)
+    except NotANumber:
+        return x
+    intpart, fraction = unexpo(intpart, fraction, expo)
+    intpart, fraction = roundfrac(intpart, fraction, digs)
+    while intpart and intpart[0] == '0': intpart = intpart[1:]
+    if intpart == '': intpart = '0'
+    if digs > 0: return sign + intpart + '.' + fraction
+    else: return sign + intpart
+
+def sci(x, digs):
+    """Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point
+    and exactly one digit before.
+    If digs is <= 0, one digit is kept and the point is suppressed."""
+    if type(x) != type(''): x = repr(x)
+    sign, intpart, fraction, expo = extract(x)
+    if not intpart:
+        while fraction and fraction[0] == '0':
+            fraction = fraction[1:]
+            expo = expo - 1
+        if fraction:
+            intpart, fraction = fraction[0], fraction[1:]
+            expo = expo - 1
+        else:
+            intpart = '0'
+    else:
+        expo = expo + len(intpart) - 1
+        intpart, fraction = intpart[0], intpart[1:] + fraction
+    digs = max(0, digs)
+    intpart, fraction = roundfrac(intpart, fraction, digs)
+    if len(intpart) > 1:
+        intpart, fraction, expo = \
+            intpart[0], intpart[1:] + fraction[:-1], \
+            expo + len(intpart) - 1
+    s = sign + intpart
+    if digs > 0: s = s + '.' + fraction
+    e = repr(abs(expo))
+    e = '0'*(3-len(e)) + e
+    if expo < 0: e = '-' + e
+    else: e = '+' + e
+    return s + 'e' + e
+
+def test():
+    """Interactive test run."""
+    try:
+        while 1:
+            x, digs = input('Enter (x, digs): ')
+            print x, fix(x, digs), sci(x, digs)
+    except (EOFError, KeyboardInterrupt):
+        pass

third_party/stdlib/test/test_fpformat.py

@@ -0,0 +1,78 @@
+'''
+   Tests for fpformat module
+   Nick Mathewson
+'''
+from test.test_support import run_unittest #, import_module
+import unittest
+# fpformat = import_module('fpformat', deprecated=True)
+import fpformat
+fix, sci, NotANumber = fpformat.fix, fpformat.sci, fpformat.NotANumber
+
+StringType = type('')
+
+# Test the old and obsolescent fpformat module.
+#
+# (It's obsolescent because fix(n,d) == "%.*f"%(d,n) and
+#                           sci(n,d) == "%.*e"%(d,n)
+#  for all reasonable numeric n and d, except that sci gives 3 exponent
+#  digits instead of 2.
+#
+# Differences only occur for unreasonable n and d.    <.2 wink>)
+
+class FpformatTest(unittest.TestCase):
+
+    def checkFix(self, n, digits):
+        result = fix(n, digits)
+        if isinstance(n, StringType):
+            n = repr(n)
+        expected = "%.*f" % (digits, float(n))
+
+        self.assertEqual(result, expected)
+
+    def checkSci(self, n, digits):
+        result = sci(n, digits)
+        if isinstance(n, StringType):
+            n = repr(n)
+        expected = "%.*e" % (digits, float(n))
+        # add the extra 0 if needed
+        num, exp = expected.split("e")
+        if len(exp) < 4:
+            exp = exp[0] + "0" + exp[1:]
+        expected = "%se%s" % (num, exp)
+
+        self.assertEqual(result, expected)
+
+    def test_basic_cases(self):
+        self.assertEqual(fix(100.0/3, 3), '33.333')
+        self.assertEqual(sci(100.0/3, 3), '3.333e+001')
+
+    @unittest.skip('grumpy')
+    def test_reasonable_values(self):
+        for d in range(7):
+            for val in (1000.0/3, 1000, 1000.0, .002, 1.0/3, 1e10):
+                for realVal in (val, 1.0/val, -val, -1.0/val):
+                    self.checkFix(realVal, d)
+                    self.checkSci(realVal, d)
+
+    def test_failing_values(self):
+        # Now for 'unreasonable n and d'
+        self.assertEqual(fix(1.0, 1000), '1.'+('0'*1000))
+        self.assertEqual(sci("1"+('0'*1000), 0), '1e+1000')
+
+        # This behavior is inconsistent.  sci raises an exception; fix doesn't.
+        yacht = "Throatwobbler Mangrove"
+        self.assertEqual(fix(yacht, 10), yacht)
+        try:
+            sci(yacht, 10)
+        except NotANumber:
+            pass
+        else:
+            self.fail("No exception on non-numeric sci")
+
+
+def test_main():
+    run_unittest(FpformatTest)
+
+
+if __name__ == "__main__":
+    test_main()