Binary search a sorted list of integers in Python 3
PEP-8

PEP-8 is a style guide for Python.
It contains several practices which you should follow, like having spaces around operators.  Use a tool, like pylint, to ensure you follow these practices.

Integer Division

mid=int((left+right)/2)


Python comes with a built-in integer division operator: //.  You should use it.

mid = (left + right) // 2


Termination

while x[mid] != y:


You are searching until you find the desired value.  What if the desired value is not present?  You will search forever???  Consider adding a different stopping condition.

Redundancy

    if x[mid]&gt;y:
        #...
        mid=int((left+right)/2)
    if x[mid]&lt;y:
        #...
        mid=int((left+right)/2)


Since you are looping while x[mid] != y, your only real choices are for x[mid] &gt; y or x[mid] &lt; y.  Instead of testing the second condition, how about using else:?

Since you enter will either the x[mid] &gt; y then clause, or the x[mid] &lt; y then clause, you will always be executing mid=int((left+right)/2).  You can safely move those two statements out if the if, and unconditionally execute it at the end.  As in:

    if x[mid] &gt; y:
        #...
    else:
        #...
    mid = (left + right) // 2


Efficiency

If you start with left=0, right=99, mid=49, and find x[mid]&gt;y is true, you proceed to search in the range left=0, right=49.  But you've already tested x[49] and found the value wasn't there; you don't need to include it in your search range anymore.  Similarly, when you find x[mid]&lt;y, you don't need to include that mid point as the left end of your range.

    if x[mid] &gt; y:
        right = mid - 1
    else:
        left = mid + 1


Bug

Your existing algorithm will not terminate for certain numbers.  If you search for 99, the value of mid will take on the following values:

49, 74, 86, 92, 95, 97, 98, 98, 98, 98, 98, 98, 98, 98, ...