To convert a decimal number to its binary equivalent you need to take the remainder of successively dividing by 2, and print in reverse. For example the number 13 is
13 / 2 = 6 rem 1
6 / 2 = 3 rem 0
3 / 2 = 1 rem 1
1 / 2 = 0 rem 1
binary = 1101
Try
nDecimal = eval(input("entrer un décimal positif :"))
print("Le nombre décimal entrer est:", nDecimal)
nbin=[]
while nDecimal > 0:
value = int(nDecimal % 2)
nDecimal = int(nDecimal / 2)
nbin.append(value)
nbin.reverse()
print("Le nombre binaire est", end=": ")
for x in nbin:
print(x, end='')