Add str.lower

[Uwe L. Korn]

• ✔️ pandas function
• ✔️ Python function
• ✔️ no need for a regular expression library
• ❌ needs a Unicode database
• ❌ cannot pre-compute output size

Pseudo-Code:

Inputs:

builder = StringBuilder()
for row in rows:
    if isnull(row)
        builder.addnull()
    else:
        builder.add(map_utf8_characters(utf8_lower))