Lookup by label using the [] operator and the .ix[] property

An implicit label lookup is performed using the [] operator. This operator normally looks up values based upon the given index labels.

Let's start by using the following Series:

A single value can be looked up using just the index label of the desired item:

Multiple items can be retrieved at once using a list of index labels:

We can also look up values using integers that represent positions:

This works purely because the index is not using integer labels. If integers are passed to [], and the index has integer values, then the lookup is performed by matching the values passed in to the values of the integer labels.

This can be demonstrated using the following Series:

The following looks up values at labels 13 and 10, not positions 13 and 10:

Lookup using the [] operator is identical to using the .ix[] property. However, .ix[] has been deprecated since pandas version 0.20.1. The reason for the deprecation is the confusion caused by integers being passed to the operators and the difference in operation depending on the type of the label in the index.

The ramifications of this is that neither [] or .ix[] should be used for lookup. Instead, use the .loc[] and .iloc[] properties, which explicitly look up by label or position only.