Python.

Format.py

def stars(format, inp):
	starct = 0
	for c in format:
		if c == '&':
			starct += 1
	numct = 0
	for c in inp:
		if not c == '.':
			numct += 1
	if starct < numct:
		print("more digits than stars")
	return '*' * (starct-numct) + inp
def commas(inp):
	#for i in range(inp.find('.')-3,0, -3): #insert comma before each of these chars at these indices
	for i in range(len(inp)-3,0, -3):
		inp = inp[0:i] + ',' + inp[i:]
	return inp

def dec(format, inp):
	decplace = len(format[format.find('.')+1:])
	print(decplace)
	decLoc = inp.find('.')
	if not decLoc == -1:
		currPlaces = len(inp[decLoc + 1:])
	else:
		decLoc = len(inp)
		inp = inp + '.'
		currPlaces = 0
	print(currPlaces)
	if(currPlaces <= decplace):
		inp = inp + '0' * (decplace-currPlaces)
	else:
		#print(inp)
		if((int(inp[decLoc + decplace + 1])) >= 5):
			inp = inp[:decLoc + decplace] + (str(int(inp[decLoc + decplace]) + 1))
		else:
			inp = inp[:decLoc + decplace+1]
	return (inp)
def dollar(inp):
	lastStarI = inp.rfind('*')
	return '$' + inp[lastStarI + 1:]
def sDollar(inp):
	lastStarI = inp.rfind('*')
	return inp[:lastStarI + 1] + '$' + inp[lastStarI +1:]
def exp(format, inp):
	oldlen = len(inp)
	if not inp.find('.') == -1:
		oldlen = len(inp[:inp.find('.')])
		inp = inp[:inp.find('.')] + inp[inp.find('.') + 1:]
	space = 0
	for c in format:
		if c == '&':
			space += 1 
	print(space)
	if space < len(inp) and int(inp[space]) >= 5: #then round
		inp = inp[:space - 1] + str(int(inp[space-1])+1)
	elif space < len(inp) and int(inp[space]) < 5:
		inp = inp[:space]
	elif space > len(inp):
		inp = inp + '0' * (space-len(inp))
	inp = inp[:1] + '.' + inp[1:] + 'E' + str(oldlen - 1)
	return inp
	
st = "&&&&E, 124353"
format, inp = st.rstrip().split(", ")[0], st.rstrip().split(", ")[1]
print(format)
if(format[-1]=='E'):
	inp = exp(format, inp)
#print(inp)
else:
	if not format.find('.') == -1:
		inp = dec(format, inp)
	#print(inp)
	inp = stars(format,inp)
	#print(inp)
	if not format.find(',') == -1:
		inp = commas(inp)
	#print(inp)
	if format[0] == '$':
		inp = dollar(inp)
	#print(inp)
	if format[0] == '*':
		inp = sDollar(inp)
	#print(inp)
print(inp)