grader.py

# This program asks for a decimal value and calculates the corresponding
# letter grade.

# Ask the user for the score.
score_as_string = input('Please enter score between 0 and 1: ')

# Convert the string returned by input() to a number.
try:
    score = float(score_as_string)
except:
    print('Please enter a number')
    quit()
    
# Ensure the score is between 0.0 and 1.0.
if score >= 0 and score <= 1:
    print('Thanks! Your grade is...')
else:
    print('Invalid Score')
    quit()
    
# Print out the calculated grade.
if score >= 0.9:
    print('A')
elif score >= 0.8:
    print('B')
elif score >= 0.7:
    print('C')
elif score >= 0.6:
    print('D')
else:
    print('F')