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My script writes to file chunk by chunk, using pre-generated data patterns:

#  Data pattern generator    
def get_random_chunk_pattern():
            return ''.join(random.choice(ascii_uppercase + digits + ascii_lowercase) for _ in range(8))
# DedupChunk class CTOR:
class DedupChunk:
    def __init__(self, chunk_size, chunk_pattern, chunk_position=0, state=DedupChunkStates.PENDING):
        self._chunk_size = chunk_size  # chunk size in bytes
        self._chunk_pattern = chunk_pattern
        self._chunk_position = chunk_position
        self._state = state
        self.mapping = None
    @property
    def size(self):
        return self._chunk_size
    @property
    def pattern(self):
        return self._chunk_pattern
    @property
    def position(self):
        return self._chunk_position
    @property
    def state(self):
        return self._state
# Here Chunk object is being initialized (inside other class's CTOR):
chunk_size = random.randint(64, 192) * 1024  # in bytes
        while (position + chunk_size) < self.file_size:  # generating random chunks number
            self.chunks.append(DedupChunk(chunk_size, DedupChunkPattern.get_random_chunk_pattern(), position))
# Actual writing
    with open(self.path, 'rb+') as f:
        for chunk in self.chunks:
            f.write(chunk.pattern * (chunk.size // 8))
PyCharm displays "Expected type 'Union[str, bytearray]'  got 'int' instead" warning in write method
But when removing the division in
f.write(chunk.pattern * chunk.size),  or doing division outside:
chunk.size //= 8
f.write(chunk.pattern * chunk.size)
warning disappeared 
What actually happened here?
Thanks
                Without knowing the contents and type of chunk.pattern, it's hard to know what's going on. Can you write chunk.pattern to file without the multiplication?
– user707650
                Oct 27, 2015 at 19:57
                I'm guessing that your chunk.pattern is somehow return an int rather than what you think it is. Try explicitly converting into a string with str(chunk.pattern *(chunk.size // 8)) and see what you get
– R Nar
                Oct 27, 2015 at 20:18
Ignore this warning. The IDE is making a best guess (from limited information) as to what the data type will be at runtime, but it is guessing wrong. That is, it is fairly reasonable to expect that something multiplied by an int will result in an int if you don't know what that something actually is.
If you really want to solve this then tell the IDE what you expect chunk.pattern to be by writing a doc string for your class (or using annotations to provide type hinting).
class DedupChunk:
    :type _chunk_pattern: str
    ... other fields
    ... # rest of class
With newer versions of python, then the preferred syntax would be:
class DedupChunk:
    def __init__(self,
            chunk_pattern: str,
            # ... more args
        self._chunk_pattern = chunk_pattern
        ... # rest of class
For local variables or class variables you can annotate the variables.
# given f() has an unknown return type
foo: str = f()  # annotate as type str and initalise
bar: str        # only annotate as type str, but leave uninitialised
class MyClass:
    foo: str = f()
    bar: str
                what if the class is an inheritance from other class, what type we should declare? I have tried to declare the type of any properties from its parent class, but the warning still there.
– oon arfiandwi
                Jun 17, 2019 at 6:11
        
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