Like other U.S. state codes, the Code of Alabama is published as a series of identically bound volumes containing the all of the laws of the state, with extensive annotations covering state and federal case law bearing on the laws' meaning and application.
Annotated state codes run to multiple volumes. Michie's Alabama Code, for example, currently comprises 39 volumes plus a softcover supplement of the most recent material; the number of volumes would have been somewhat fewer in Atticus Finch's day, but it still would have filled a couple of shelves of a good-size bookcase and perhaps spilled over onto a third shelf.
Any solo lawyer practicing in a particular state in those days would have been very likely to own (and display) the annotated state code set, not just a single book. The fact that Finch's volumes were "unsullied" suggests that they adorned his shelves more for show than for practical research. This isn't because he was a bad lawyer; it's because most of the day-to-day business that small-town lawyers perform consists of applying settled law and rote procedures.
One of the most sobering moments in a U.S. law school student's early encounters with the law library involves looking at the shelves and shelves of annotated state codes for the various states in the Union. It is truly a daunting sight.