Level 9 · Route a refund from the web form

What type is this value?

Every value in Python has a type, and type() tells you which one:

type(10482)        # <class 'int'>
type("3")          # <class 'str'>
type(24.99)        # <class 'float'>
type("3").__name__ # 'str'  just the name, handy in a report

Data from a web form, a CSV opened by hand or an API usually arrives as text, even when it looks like a number. Text and numbers don’t mix: "3" * 2 is "33" (the text repeated), and "3" * "24.99" raises a TypeError. When a calculation gives a strange answer, type() is the first thing to check.

Converting between types

int(), float() and str() build a new value of the type you ask for:

int("3")             # 3
float("24.99")       # 24.99
int("3") * float("24.99")   # 74.97 (after rounding to 2)
str(10482)           # '10482'
"Order " + str(10482)       # 'Order 10482'

+ between two strings joins them, but "Order " + 10482 fails because one side is an int. Convert with str() or use an f-string, which converts for you. Conversions can fail too: int("3.0") and float("n/a") raise ValueError, which is often how you discover a bad row.

match and case

When one value decides between several fixed options, match reads more cleanly than a long if/elif chain. Python compares the value with each case from top to bottom and runs the first one that fits:

match "WRG":
    case "DMG" | "WRG":     # | means "either of these"
        queue = "warehouse"
    case "LATE":
        queue = "carrier"
    case _:                 # _ catches everything else
        queue = "manual"

Each case lists a value to compare with, and the first one that matches wins, so order still matters if two cases could overlap. Compared with if code == "DMG" or code == "WRG": ... elif ..., the match version names the value once and lays the options out like the routing table Angela sent, which makes it easy to check against the policy line by line.

case _ is the safety net, like a final else. Without it, an unknown code would leave queue unset and the next line would fail with a NameError. match needs Python 3.10 or newer, which is what runs here.

Common mistakes

• Multiplying the texts directly. Convert first, then calculate.
• Matching the raw input. Clean it with .strip().upper() so ” wrg” and “WRG” are treated the same.
• Forgetting case _, so an unexpected code leaves the queue undefined.
• Joining a number into text with + without str().