John Cook: Searching Greek and Hebrew with regular expressions

According to the Python Cookbook, “Mixing Unicode and regular expressions is often a good way to make your head explode.” It is thus with fear and trembling that I dip my toe into using Unicode with Greek and Hebrew.

I heard recently that there are anomalies in the Hebrew Bible where the final form of a letter is deliberately used in the middle of a word. That made me think about searching for such anomalies with regular expressions. I’ll come back to that shortly, but I’ll start by looking at Greek where things are a little simpler.

Greek

Only one letter in Greek has a variant form at the end of a word. Sigma is written ς at the end of a word and σ everywhere else. The following Python code shows we can search for sigmas and final sigmas in the first sentence from Matthew’s gospel.

    import re

    matthew = "Κατάλογος του γένους του Ιησού Χριστού, γιου του Δαυείδ, γιου του Αβραάμ"
    matches = re.findall(r"\w+ς\b", matthew)
    print("Words ending in sigma:", matches)

    matches = re.findall(r"\w*σ\w+", matthew)
    print("Words with non-final sigmas:", matches)

This prints

    Words ending in sigma: ['Κατάλογος', 'γένους']
    Words with non-final sigmas: ['Ιησού', 'Χριστού']

This shows that we can use non-ASCII characters in regular expressions, at least if they’re Greek letters, and that the metacharacters \w (word character) and \b (word boundary) work as we would hope.

Hebrew

Now for the motivating example. Isaiah 9:6 contains the word “לםרבה” with the second letter (second from right) being the final form of Mem, ם, sometimes called “closed Mem” because the form of the letter ordinarily used in the middle of a word, מ, is not a closed curve.

Here’s code to show we could find this anomaly with regular expressions.

    # There are five Hebrew letters with special final forms.
    finalforms = "\u05da\u05dd\u05df\u05e3\u05e5" # ךםןףץ

    lemarbeh = "\u05dc\u05dd\u05e8\u05d1\u05d4" # לםרבה
    m = re.search(r"\w*[" + finalforms + "\w+", lemarbeh)
    if m:
        print("Anomaly found:", m.group(0))

As far as I know, the instance discussed above is the only one where a final letter appears in the middle of a word. And as far as I know, there are no instances of a non-final form being used at the end of a word. For the next example, we will put non-final forms at the end of words so we can find them.

We’ll need a list of non-final forms. Notice that the Unicode value for each non-final form is 1 greater than the corresponding final form. It’s surprising that the final forms come before the non-final forms in numerical (Unicode) order, but that’s how it is. The same is true in Greek: final sigma is U+03c2 and sigma is U+03c3.

    finalforms = "\u05da\u05dd\u05df\u05e3\u05e5" # ךםןףץ
    nonfinal   = "\u05db\u05de\u05e0\u05e4\u05e6" # כמנפצ

We’ll start by taking the first line of Genesis

    genesis = "בראשית ברא אלהים את השמים ואת הארץ" 

and introduce errors by replacing each final form with its corresponding non-final form. The code uses a somewhat obscure feature of Python and is analogous to the shell utility tr.

    genesis_wrong = genesis.translate(str.maketrans(finalforms, nonfinal))

(The string method translate does what you would expect, except that it takes a translation table rather than a pair of strings as its argument. The maketrans method creates a translation table from two strings.)

Now we can find our errors.

    anomalies = re.findall(r"\w+[" + nonfinal + r"]\b", genesis_wrong)
    print("Anomalies:", anomalies)

This produced

    Anomalies: ['אלהימ', 'השמימ', 'הארצ']

Note that Python printed the letters left-to-right.

Python

I started this post with a warning from the Python Cookbook that mixing regular expressions and Unicode can cause your head to explode. So far my head intact, but I’ve only tested the waters. I’m sure there are dragons in the deeper end.

I should include the rest of the book’s warning. I used the default library re that ships with Python, but the authors recommend if you’re serious about using regular expressions with Unicode,

… you should consider installing the third-party regex library which provides full support for Unicode case folding, as well as a variety of other interesting features, including approximate matching.

Related posts

• Python regular expressions
• Hebrew in LaTeX
• The hopeless task of Unicode

The post Searching Greek and Hebrew with regular expressions first appeared on John D. Cook.

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