Python Intermediate Lesson 6: Regular Expressions for UPI, GSTIN and PAN

📎 This article includes 3 downloadable practice files ↓

📘 Python Intermediate Course · Lesson 6 of 10

A regular expression describes the shape of text. Python’s re module matches, extracts and replaces with it.

Parse a UPI narration with named groups

UPI = re.compile(r"^UPI/(?P<dir>DR|CR)/(?P<ref>\d{12})/(?P<payee>[^/]+)/"
                 r"(?P<bank>[A-Z]{4})/(?P<vpa>[^/]+)/(?P<note>.*)$")
m = UPI.match("UPI/DR/412345678901/SWIGGY/YESB/swiggy@ybl/Dinner")
m["payee"], m["vpa"], m["ref"]     # 'SWIGGY', 'swiggy@ybl', '412345678901'

Validate GSTIN and PAN

GSTIN = re.compile(r"^\d{2}[A-Z]{5}\d{4}[A-Z][1-9A-Z]Z[0-9A-Z]$")
PAN   = re.compile(r"^[A-Z]{5}\d{4}[A-Z]$")

A GSTIN is a 2-digit state code, the 10-character PAN, an entity number, the letter Z and a check character. The pattern checks the shape, not whether the GSTIN is registered or the check digit is right; use the GST portal for that.

Common mistakes

• match vs search: match anchors at the start; search looks anywhere.
• Greedy .* swallows too much; prefer [^/]+ style classes.

Practice

Unzip the practice data into a folder, put this lesson’s script in the same folder and run it (python pyi-NN.py). Compare with the expected output file. Then change one thing (a filter, a column, a format) and predict the new output before you run it.