This is a basic exercise on using loops.

######################Free Code###########################
##  good old == is fine for everything else.
def close_enough(x,y):
    """prec: x, y are numbers
    postc: returns True if x and y are close enough for
    our purposes. use this to check for "equality" of
    floating-point numbers."""
    return abs(x - y) < 1e-6
######################Problem 0###########################
def meanie(x):
    """prec: x is non-empty numerical list
    postc:  returns the mean of x."""
    total = 0
    for k in x:
        total += k
    return total/len(x)
######################Problem 1###########################
def count_down(n):
    """prec: n is an integer and n >= 0
    post:  returns a countdown string. FOr example
    count_down(10) returns "10 9 8 7 6 5 4 3 2 1 0 Blastoff!"
    """
    return ""
######################Problem 2###########################
def trimmed_sum(x, a):
    """prec: x is a numerical list, and a is a number
postc:  computes the sum of all value in the list x
that are <= a."""
    return 0
######################Problem 3###########################
def median(x):
    """precondition:  x is a numerical list
    postcondtion:  returns the median of x.  This is the 
    middle value in numerical order if the length is odd and the
    average of the two middle values if the length is even."""
    return 0
######################Problem 4###########################
def sigma(f, n):
    """precondition:  f is a function defined on the nonnegative
    integers, and n is a nonnegative integer.
    postcondition: returns sum(f(k), k = 0..n)."""
    return 0
######################Problem 5###########################
def seek_string(quarry, file_name):
    """precondition:  quarry and file_name are strings
    postcondtion:  if the file named by file_name does not
    exist, return the string "(file_name) not found."  
    If it does, return a list containing all lines of 
    the file in which the string quarry is a substring of the line."""
if __name__ == "__main__":
    #This is what my testing code looks like.
    #feel free to crib it and bend it to your purposes.
    print("****************** Test Problem 0****************")
    x = [1,2,3,4,5,6]
    y = 3.5
    print(f"Case x = {x}:  ", end = "")
    print("PASS" if close_enough(meanie(x),y) else "FAIL")
    x = [-2, -1, 0, 1, 2]
    y = 0
    print(f"Case x = {x}:  ", end = "")
    print("PASS" if close_enough(meanie(x),y) else "FAIL")

In case you have forgotten, it's very easy to iterate through a file a line at a time. Download the file linewise.py to see how to do this.