Pygame argument 2 must be pygame.surface not str

Question

My code so far, the problem I have is that when I enter the sprite from the selection, I get an error stating that the argument must be surface not string. I am wondering how to fix this. What I am trying to do is have the user select a sprite from the following, SP1R, SP1O etcetera. But after I input one of the sprites, the program does not accept it and it gives the following error:

Traceback (most recent call last):  
File "C:\Users\User\Documents\Pygame\pygame1.py", line 90, in <module>
drawGrid()  
File "C:\Users\User\Documents\Pygame\pygame1.py", line 60, in drawGrid
win.blit (UserSprite, (500, 500))  
TypeError: argument 1 must be pygame.Surface, not str

import pygame #Imports pygame
pygame.init() #Initialises pygame

win = pygame.display.set_mode((700, 700)) #Sets window size

pygame.display.set_caption("T1") #Sets title to T1

SP1R = pygame.image.load('Sprite 1 Red.png')
SP1O = pygame.image.load('Sprite 1 Orange.png')
SP1Y = pygame.image.load('Sprite 1 Yellow.png')
SP1G = pygame.image.load('Sprite 1 Green.png')
SP1B = pygame.image.load('Sprite 1 Blue.png')
SP1PU = pygame.image.load('Sprite 1 Purple.png')
SP1PI = pygame.image.load('Sprite 1 Pink.png')
SP2R = pygame.image.load('Sprite 2 Red.png')
SP2O = pygame.image.load('Sprite 2 Orange.png')
SP2Y = pygame.image.load('Sprite 2 Yellow.png')
SP2G = pygame.image.load('Sprite 2 Green.png')
SP2B = pygame.image.load('Sprite 2 Blue.png')
SP2PU = pygame.image.load('Sprite 2 Purple.png')
SP2PI = pygame.image.load('Sprite 2 Pink.png')
SP3R = pygame.image.load('Sprite 3 Red.png')
SP3O = pygame.image.load('Sprite 3 Orange.png')
SP3Y = pygame.image.load('Sprite 3 Yellow.png')
SP3G = pygame.image.load('Sprite 3 Green.png')
SP3B = pygame.image.load('Sprite 3 Blue.png')
SP3PU = pygame.image.load('Sprite 3 Purple.png')
SP3PI = pygame.image.load('Sprite 3 Pink.png')

x = 300 #x character position set to 50
y = 520 #y character position set to 50
width = 64 #width set to 40
height = 64 #height set to 60
vel = 10 #Character speed set to 5
white = (255, 255, 255)
left = False
right = False
UserSprite = input("""Choose a sprite the options are
SP1R, SP1O, SP1Y, SP1G, SP1B, SP1PU, SP1PI
SP2R, SP2O, SP2Y, SP2G, SP2B, SP2PU, SP2PI
SP3R, SP3O, SP3Y, SP3G, SP3B, SP3PU, SP3PI""")
while UserSprite != (SP1R or SP1O or SP1Y or SP1G or SP1B or SP1PU or SP1PI or SP2R or SP2O or SP2Y or SP2G or SP2B or SP2PU or SP3PI or SP3R or SP3O or SP3Y or SP3G or SP3B or SP3PU or SP3PI):
    print ("Nope")
    break


def drawGrid():
    win.fill((0, 0, 0))
    if left:
        win.blit(walkLeft)#draws the following sprites
    elif right:
        win.blit(walkRight)
    pygame.display.update() #updates the display by doing the above
    pygame.draw.line(win, white, [50,50], [50, 600], 5)
    pygame.draw.line(win, white, [50,50], [600, 50], 5)
    pygame.draw.line(win, white, [600,600], [600, 50], 5)
    pygame.draw.line(win, white, [50,600], [600, 600], 5)
    pygame.draw.line(win, white, [50,450], [600, 450], 5)
    pygame.display.update()
    win.blit (UserSprite, (500, 500))

run = True #sets run to true
while run: #While loop for above
    pygame.time.delay(100) #Sets a delay to prevent crashing

    for event in pygame.event.get(): #For loop for event

        if event.type == pygame.QUIT: #If user quits window
            run = False #Do not run

    keys = pygame.key.get_pressed()#Sets keybinds

    if keys[pygame.K_a] and x>55:
        x -= vel
        left = True
        right = False
    elif keys[pygame.K_d] and x <575:
        x += vel
        right = True
        left = False
    if keys[pygame.K_w] and y >455:
        y -= vel
        up = True
        down = False
    elif keys[pygame.K_s] and y <565:
        y += vel
        down = True
        up = False

drawGrid()

Answer 1

After the input

UserSprite = input("""Choose a sprite [...]""")

the content of the variable UserSprite is a string. You have to find the variable with the name, which is stored in the variable UserSprite.
You can get the dictionary with the local variables by the built in function vars(), when you call it without any parameter. This means vars()["SP1R"] will return the object SP1R.

SpriteName = input("""Choose a sprite [...]""")
UserSprite = vars()[SpriteName] if SpriteName in vars() else None