[Python] Python cannot search Chinese string in file [duplicate]

I have the following text file named "test_data.txt":

一行出去就係泳池，再行出啲就係沙灘。
關


And I have the following code to check if the wording "關" is included in the text file:

data = open('test_data.txt', 'r')
if '關' in data:
print("yes")
else:
print("no")


It prints:

no
​

How come? What did I miss?

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