Making a number list in a .txt file

[volcano63]

f=open("dico.txt","w")
a=0
while a<=999999:
	if a<=99999:
		def add_zero(nbr: str, m: int = 6) -> str:
			return "0" * (m - len(nbr)) + nbr
	f.write(str(a))
	a=a+1
	else:
    f.write(str(a))
	a=a+1
f.close()

A syntax error in the "else" line appears.

Could you tell me why?

Because your indents are off - but as I understand, you are trying to write 0-padded values to a file, so you define a function for it (in a very inefficient way, I must add) and then you never call it.

The proper - and much easier way would be to use formatting - if you number is called number - one-letter names is a bad practice - f'{number:06d} will do the trick in Python versions 3.6 and above. Up to 3.5, '{:06d}'.format(number) will do.