# Computational biology at CSU

assignment2

## ASSIGNMENT 2

Due date: 10/2/18 by 10 am

The exercises can be completed using only material covered so far.

### Exercise 1

Write a function called `nt_id()` that evaluates whether or not a sequence entered by the user is DNA or RNA or unknown.

The sequence should be passed to the function and the return value printed as follows:

```if __name__ == '__main__':
seq = input('Enter a sequence: ')
print(nt_id(seq))```

`if name == 'main':` basically means to execute the code within the body of the `if` statement only if the file is executed from the command line as a script.

### Exercise 2

Write a function called `stop_codon()` that tests for the presence of a stop codon (UAG, UAA, and UGA) in an RNA sequence and returns a Boolean value indicating whether the sequence contains a stop codon. The sequence should be passed to the function as in 1.

### Exercise 3

Write a function called `peptide_length()` that computes the maximum peptide length (an integer) that can be generated from a DNA or RNA sequence input by the user.

### Exercise 4

Write a function called `cube_root()` that computes the cube root of a number. The function should contain a try and except clause that returns an informative error message if a non-numerical value is entered.

Hints:
1) Reassign the value input by the user to a float type in the `cube_root()` function, not in the input function.
2) The return value should be the cube root of the number if a valid number is entered or an error message if a valid number is not entered.

### Exercise 5

Write a function called `sum_num()` that computes the sum of up to 4 numbers. You do not need to prompt the user for the numbers.

### Exercise 6

Write a script that prompts the user for an RNA sequence, imports the module containing the `stop_codon()` function from exercise 2 and tests for the presence of a stop codon in the sequence. The script should print a message indicating whether the sequence contains a stop codon based on the return value of `stop_codon()`.

To submit your assignment, combine the functions in exercise 1-5 along with the script in exercise 6 into one text file and upload it to Canvas. 