Python: isdigit() vs. isdecimal()

The difference between str.isdigit() and str.isdecimal() in Python is, for most of us, academic and can be used interchangeably. According to the Python documentation, the decimal category “includes digit characters, and all characters that can be used to form decimal-radix numbers, e.g. U+0660, ARABIC-INDIC DIGIT ZERO.”

So, all decimals are digits, but not all digits are decimals. It turns out that most are though. Here’s a small Python script that returns the Unicode characters that are decimals but not digits.

import unicodedata
count=1
digitcount=0
decimalcount=0
print("#","Integer","Unicode Name","Character","HTML",sep="\t")
for i in range(1,1114111):
    if chr(i).isdigit() and not chr(i).isdecimal():
        try:
            print(count,i,unicodedata.name(chr(i)),chr(i), "" + str(i) + ";",sep="\t")
        except:
            print("??", "" + str(i) + ";",sep="\t")
        count=count+1
    if chr(i).isdigit():
        digitcount=digitcount+1
    if chr(i).isdecimal():
        decimalcount=decimalcount+1
    
print("digit count:",digitcount)
print("decimal count:",decimalcount)

Note that some of the characters cannot be printed out in the Python Shell or in the browser. The table shows both the character from the Python Shell (when possible) and the HTML char ref.

Of the 1,114,111 Unicode characters, there are 588 digits, 460 of which are also decimals. So, there you are. 🙂

So, which should you use? It doesn’t make much difference really, but isdigit() is the most popular, perhaps because the name most closely matches the intention of the function.