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Given the following text description, write Python code to implement the functionality described.
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Description:
Change numerical base of input number x to base.
    return string representation after the conversion.
    base numbers are less than 10.
    
This is how the function will work:
 change_base(8, 3)
    '22'
    
This is how the function will work:
 change_base(8, 2)
    '1000'
    
This is how the function will work:
 change_base(7, 2)
    '111'
    
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Python Code:
def change_base(x: int, base: int):
    
    ret = ""
    while x > 0:
        ret = str(x % base) + ret
        x //= base
    return ret
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