Initial revision

Lib/fpformat.py

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+# 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
+
+
+import regex
+
+# Compiled regular expression to "decode" a number
+decoder = regex.compile( \
+	'^\([-+]?\)0*\([0-9]*\)\(\(\.[0-9]*\)?\)\(\([eE][-+]?[0-9]+\)?\)$')
+# \0 the whole thing
+# \1 leading sign or empty
+# \2 digits left of decimal point
+# \3 fraction (empty or begins with point)
+# \5 exponent part (empty or begins with 'e' or 'E')
+
+NotANumber = 'fpformat.NotANumber'
+
+# 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
+def extract(s):
+	if decoder.match(s) < 0: raise NotANumber
+	(a1, b1), (a2, b2), (a3, b3), (a4, b4), (a5, b5) = decoder.regs[1:6]
+	sign, intpart, fraction, exppart = \
+		s[a1:b1], s[a2:b2], s[a3:b3], s[a5:b5]
+	if sign == '+': sign = ''
+	if fraction: fraction = fraction[1:]
+	if exppart: expo = eval(exppart[1:])
+	else: expo = 0
+	return sign, intpart, fraction, expo
+
+# Remove the exponent by changing intpart and fraction
+def unexpo(intpart, fraction, expo):
+	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
+
+# Round or extend the fraction to size digs
+def roundfrac(intpart, fraction, 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, ''
+
+# Format x as [-]ddd.ddd with 'digs' digits after the point
+# and at least one digit before.
+# If digs <= 0, the point is suppressed.
+def fix(x, digs):
+	if type(x) != type(''): x = `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
+
+# 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.
+def sci(x, digs):
+	if type(x) != type(''): x = `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 = `abs(expo)`
+	e = '0'*(3-len(e)) + e
+	if expo < 0: e = '-' + e
+	else: e = '+' + e
+	return s + 'e' + e
+
+# Interactive test run
+def test():
+	try:
+		while 1:
+			x, digs = input('Enter (x, digs): ')
+			print x, fix(x, digs), sci(x, digs)
+	except (EOFError, KeyboardInterrupt):
+		pass