[FIXED] Why do I get an IndentationError using %time in IPython for a multi-line expression?

Issue

When I try to run this code I get following error.

IndentationError: unindent does not match any outer indentation level

It seems strange to me because I think this code worked before. the error appears with parentheses in 18 lines. it also seems that everything is OK with parentheses, just like spaces

%time
# This can take some time…
min_mae = float("Inf")
best_params = None
for eta in [.3, .2, .1, .05, .01, .005]:
    print("CV with eta={}".format(eta))
    # We update our parameters
    params['eta'] = eta
    # Run and time CV

    %time cv_results = xgb.cv(
            params,
            dtrain,
            num_boost_round=num_boost_round,
            seed=42,
            nfold=5,
            metrics=['mae'],
            early_stopping_rounds=10
          )

    # Update best score
    mean_mae = cv_results['test-mae-mean'].min()
    boost_rounds = cv_results['test-mae-mean'].argmin()
    print("\tMAE {} for {} rounds\n".format(mean_mae, boost_rounds))
    if mean_mae < min_mae:
        min_mae = mean_mae
        best_params = eta

print("Best params: {}, MAE: {}".format(best_params, min_mae))

Solution

The %time line magic doesn't work like that with split lines. You either have to write your expression on a single line or add an explicit \ at the end of each line to escape the linebreak:

%time cv_results = xgb.cv(\
        params, \
        dtrain, \
        num_boost_round=num_boost_round, \
        seed=42, \
        nfold=5, \
        metrics=['mae'], \
        early_stopping_rounds=10 \
      )

Also, assuming your first line is meant to measure the execution time of the full code, you need to use the cell magic %%time instead of %time.

Answered By - jhansen