<SYSTEM_TASK:>
Given the following text description, write Python code to implement the functionality described below step by step
<END_TASK>
<USER_TASK:>
Description:
 Project Euler
Step2:  First write a number_to_words(n) function that takes an integer n between 1 and 1000 inclusive and returns a list of words for the number as described above
Step3:  Now write a set of assert tests for your number_to_words function that verifies that it is working as expected.
Step5:  Now define a count_letters(n) that returns the number of letters used to write out the words for all of the the numbers 1 to n inclusive.
Step6:  Now write a set of assert tests for your count_letters function that verifies that it is working as expected.
Step7:  Finally used your count_letters function to solve the original question.
<ASSISTANT_TASK:>
Python Code:
number={}
number[0]="zero"
number[1]="one"
number[2]="two"
number[3]="three"
number[4]='four'
number[5]='five'
number[6]='six'
number[7]='seven'
number[8]='eight'
number[9]='nine'
number[10]='ten'
number[11]='eleven'
number[12]='twelve'
number[13]='thirteen'
number[14]='fourteen'
number[15]='fifteen'
number[16]='teen'
number[20]='twenty'
number[30]='thirty'
number[40]='forty'
number[50]='fifty'
number[60]='sixty'
number[70]='seventy'
number[80]='eighty'
number[90]='ninety'
number[17]='and'
number[100]='hundred'
number[1000]='thousand'
Explanation: Project Euler: Problem 17
https://projecteuler.net/problem=17
If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total.
If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?
NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and forty-two) contains 23 letters and 115 (one hundred and fifteen) contains 20 letters. The use of "and" when writing out numbers is in compliance with British usage.
End of explanation
num=[]
def number_to_words(n):
    Given a number n between 1-1000 inclusive return a list of words for the number.
    if n<16:
        return number[n]
    if n>15 and n<20:
        num=number[n-10]+number[16]
        return num
    if n>19 and n<31:
        num=number[20]+number[n-20]
        return num
    if n>29 and n<41:
        num=number[30]+number[n-30]
        return num    
    if n>39 and n<51:
        num=number[40]+number[n-40]
        return num    
    if n>49 and n<61:
        num=number[50]+number[n-50]
        return num
    if n>59 and n<71:
        num=number[60]+number[n-60]
        return num    
    if n>69 and n<81:
        num=number[70]+number[n-70]
        return num   
    if n>79 and n<91:
        num=number[80]+number[n-80]
        return num
    if n>89 and n<101:
        num=number[90]+number[n-90]
        return num    
    if n>99 and n<200:
        num= number[1]+number[100]+ number[17] + number_to_words(n-100)
        return num
    if n>199 and n<300:
        num= number[2]+number[100]+ number[17] + number_to_words(n-200)
        return num    
    if n>299 and n<400:
        num= number[3]+number[100]+ number[17] + number_to_words(n-300)
        return num
    if n>399 and n<500:
        num= number[4]+number[100]+ number[17] + number_to_words(n-400)
        return num   
    if n>499 and n<600:
        num= number[5]+number[100]+ number[17] + number_to_words(n-500)
        return num
    if n>599 and n<700:
        num= number[6]+number[100]+ number[17] + number_to_words(n-600)
        return num    
    if n>699 and n<800:
        num= number[7]+number[100]+ number[17] + number_to_words(n-700)
        return num
    if n>799 and n<900:
        num= number[8]+number[100]+ number[17] + number_to_words(n-800)
        return num    
    if n>899 and n<1000:
        num= number[9]+number[100]+ number[17] + number_to_words(n-900)
        return num
# number
# len(number[100])
number_to_words(767)
Explanation: First write a number_to_words(n) function that takes an integer n between 1 and 1000 inclusive and returns a list of words for the number as described above
End of explanation
# YOUR CODE HERE
assert number_to_words(342)=='threehundredandfortytwo'
assert number_to_words(115)=='onehundredandfifteen'
assert True # use this for grading the number_to_words tests.
Explanation: Now write a set of assert tests for your number_to_words function that verifies that it is working as expected.
End of explanation
def count_letters(n):
    Count the number of letters used to write out the words for 1-n inclusive.
    count=0
    while n>0:
        L=number_to_words(n)
        count=count+len(L)
        n=n-1
    return count
count_letters(115)
Explanation: Now define a count_letters(n) that returns the number of letters used to write out the words for all of the the numbers 1 to n inclusive.
End of explanation
# YOUR CODE HERE
assert count_letters(5)==19 
assert count_letters(10)==39
assert True # use this for grading the count_letters tests.
Explanation: Now write a set of assert tests for your count_letters function that verifies that it is working as expected.
End of explanation
# YOUR CODE HERE
count_letters(999)
Explanation: Finally used your count_letters function to solve the original question.
End of explanation
<END_TASK>