Python string frequency program

[Florrianer]

x = raw_input("Enter string: ")  

def frequencies(x):
    d = dict()      
    for c in x:     
        if c not in d:      
            d[c] = 1        
        else:
            d[c] += 1       
    return d

How can one rewrite this code to perform the same function for a textfile instead?

[andrean]

filename = 'readlines.txt'
with open(filename, 'r') as text_file:
    x = text_file.read()
    
def frequencies(x):
    d = dict() 
    for c in x: 
        if c not in d: 
            d[c] = 1 
        else:
            d[c] += 1 
    return d 

print frequencies(x)