So if you had the sentence “This looks like a tree” and you look for the pattern “^This” it will successfully match since “This” is in the beginning. The caret (^) looks for a pattern that starts the string or text.Finally, we have two characters that reference the specific position of a pattern. Let’s say the pattern you’re looking for is “h.s”: this means any character ranging from a letter, a number, or a special character can be between the “h” and the “s”. Now let’s get into something special: we can actually use the period (.) to represent any character other than a newline character, which creates indentations. The two different applications of regular expressions are no different from entering a regular string. If you’re looking for a phrase, a part of a word, or a whole word such as “was”, then you can write exactly “was”. So let’s say you’re looking for occurrences of the letter “e”: you can exactly write “e”. Just like regular strings, the patterns always start and end with double quotations (“”). Let’s go through some of the important meta-characters used to type out the patterns we need to look for. Also, when dealing with numbers, you will never deal with more than one digit at a time, since there isn’t a single character that represents anything beyond 0 through 9. The format of a phone number is a very specific pattern of numbers and hyphens and more than just a single character – the general syntax of which we’ll discuss next.įirst, it should be quickly noted that regex is generally case-sensitive: the letter “a” and the letter “A” would be considered to be separate characters. You could also look through text specifically for phone numbers (#-#-#). On the other hand, in a string that read you could choose to look only for the letters within that string. This is the most basic application of regular expressions: you can look for only alphabetic characters in strings mixed with letters, numbers, and special characters. For example, if you search for the letter “f” in the sentence “For the love of all that is good, finish the job,” the goal is to look for occurrences of the character “f” in the sentence. This concept can apply to simple words, phone numbers, email addresses, or any other number of patterns. In fact, REGEX is actually just short for regular expressions, which refer to the pattern of characters used in a string. REGEX is a module used for regular expression matching in the Python programming language. Choosing between re.match and re.search.Using characters to create indentations.If you want a really complete treatment of this topic, this is the resource for you.įor some examples of string manipulation and regular expressions in action at a larger scale, see Pandas: Labeled Column-oriented Data, where we look at applying these sorts of expressions across tables of string data within the Pandas package. Mastering Regular Expressions (OReilly, 2006) is a 500+ page book on the subject.Python's official regular expression HOWTO: a more narrative approach to regular expressions in Python.Now that I have the basics down, I have found this page to be an incredibly valuable resource to recall what each specific character or sequence means within a regular expression. Python's re package Documentation: I find that I promptly forget how to use regular expressions just about every time I use them.If you'd like to learn more, I recommend the following resources: The above discussion is just a quick (and far from complete) treatment of this large topic. ipynb) with "Python" in their filename by using the " *" wildcard to match any characters in between:įurther Resources on Regular Expressions ¶ If you frequently use the command-line, you are probably familiar with this type of flexible matching with the " *" character, which acts as a wildcard.įor example, we can list all the IPython notebooks (i.e., files with extension. I'll suggest some references for learning more in Further Resources on Regular Expressions.įundamentally, regular expressions are a means of flexible pattern matching in strings. My goal here is to give you an idea of the types of problems that might be addressed using regular expressions, as well as a basic idea of how to use them in Python. Friedl’s Mastering Regular Expressions, 3rd Edition), so it will be hard to do justice within just a single subsection. Regular expressions are a huge topic there are there are entire books written on the topic (including Jeffrey E.F. The methods of Python's str type give you a powerful set of tools for formatting, splitting, and manipulating string data.īut even more powerful tools are available in Python's built-in regular expression module. Flexible Pattern Matching with Regular Expressions ¶
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