Calculate knight moves
Review

There are a few things that can be improved upon here,


  def letterNumberSwap(x):



is reinventing the wheel of str.index()
and str[index]



  randomStart = str(letterNumberSwap(randint(1,8)))+str(randint(1,8))



random.choice() might be better choice :)


  It's just implementation details. randint delegates to randrange, so it has another layer of function call overhead, and randrange goes through a lot of argument checking and other crud. In contrast, choice is a really simple one-liner. source




moveList = [] # list of moves in matrix connotation
possibleMoves = [] # list of moves in chess connotation




Stick to the scope. 

Do not make these globals,.. either return or yield them from the function



if (0 &lt; (c - 2) &lt;= 8):
    if (0 &lt; (r - 1) &lt;= 8):
        moveList.append([c - 2, r - 1])
    if (0 &lt; (r + 1) &lt;= 8):
        moveList.append([c - 2, r + 1])




Stick to DRY, you can avoid the repetition by saving all possible directions in a list
Don't do string + string but use .format() or use the fancy f"{string}" if you use python 3.6+ 
in range(x) is alot faster in python3 instead of x &lt;= !! and x &gt;= !! @Graipher
Naming 

In chess a row is called a rank, and a collumn is called a file
Avoid magic numbers

Make the WIDTH and HEIGHT constant so that they can easily be changed


Alternative

from string import ascii_uppercase
from random import choice

BOARD_HEIGHT = 5
BOARD_WIDTH = 13
CHESS_FILES = ascii_uppercase[:BOARD_WIDTH]
CHESS_RANKS = range(1, BOARD_HEIGHT+1)

def knight_moves(file, rank):
    position = (CHESS_FILES.index(file), rank)
    directions = ((1, 2), (1, -2), (-1, 2), (-1, -2), (2, 1), (2, -1), (-2, 1), (-2, -1))

    for direction in directions:
        file, rank = (d + p for d, p in zip(direction, position))
        if  file in range(BOARD_WIDTH) and rank in CHESS_RANKS:
            yield f"{CHESS_FILES[file]}{rank}"

if __name__ == '__main__':
    file = choice(CHESS_FILES)
    rank = choice(CHESS_RANKS)

    print(f"With BOARD({BOARD_WIDTH}, {BOARD_HEIGHT})")
    print(f"A knight on {file}{rank} can go to:")
    print(", ".join(knight_moves(file, rank)))