Python, Pandas, I have a dataframe containing datetimes and values.

# Create an empty DataFrame with 'timestamp' and 'value' columns
df = pd.DataFrame(columns=['timestamp', 'value'])
df.set_index('timestamp', inplace=True)

I append data to that frame over time.

At some point, I want to find the value at a timestamp. If it’s already in the df, great, easy to find.

However, if the time I’m looking for is between two existing values, how can I find that quickly, and interpolate between those two bracketing values? ChatGPT led me on a merry chase with nothing by invalid comparisons.

Here’s what I tried so far, not working:

                # Check if the target timestamp exists in the DataFrame
                timestamps = df.index
                if target_timestamp in timestamps:
                    # Exact match found
                    return df.loc[target_timestamp, 'value']
                else:
                    # Use searchsorted to find the insertion point
                    pos = timestamps.searchsorted(target_timestamp)

                    if pos == 0 or pos == len(timestamps) - 1:
                        raise ValueError("Target timestamp is out of bounds for interpolation")

                    if target_timestamp > timestamps[pos]:
                        previous_timestamp = timestamps[pos]
                        next_timestamp = timestamps[pos + 1]
                    else:
                        previous_timestamp = timestamps[pos - 1]
                        next_timestamp = timestamps[pos]

                    # Interpolating the value
                    previous_value = df.loc[previous_timestamp, 'value']
                    next_value = df.loc[next_timestamp, 'value']

                    # Linear interpolation formula
                    interpolated_value = previous_value + (next_value - previous_value) * 
                                        (target_timestamp - previous_timestamp) / (next_timestamp - previous_timestamp)

                    return interpolated_value