Regex special characters password#
This pattern is used to check if a password meets the following criteria. Here we have a regular expression regex_pattern as a String. When we create an instance of the Pattern class, we pass the regular expression as a string.
The Pattern class represents a regular expression. In this example, we used the Pattern and Matcher classes from the package. , +, *, ?, ^, $, (, ),, matches aaa, aaaa, aaaaa ? Matches the preceding element zero or one time ab?c matches ac, abc + Matches the preceding element one or more times ab+c matches abc, abbc, abbbc, etc., but not ac \| the choice operator, it matches either the expression before or expression after the operator \| ab\|def matches either ab or def \ Escape or backslash common escape sequences like \n or newline, \t for tab Example of Using Regex Special Characters in Java Regular expressions make use of special characters such as. Regex is a type of textual syntax representing patterns for text matching. Special Characters in Java Regular Expressions We’ll look at how special characters are utilized in regex. It simplifies and reduces the number of lines in a program. Regex (Regular Expression) is a useful tool for manipulating, searching, and processing text strings.
In turn, the regex engine got the pattern “number1, following by the number 3, right next to a word boundary, followed by a space, followed by the number 5” and it found a match in 13 57, as it should.
What happened was Python got a raw string, it suppressed \b's special meaning, so the value remained equal 13\b 5 and this is what was passed to the regex engine. This happened because raw strings just told Python to suppress the special meaning (we saw this in the bullet point above, in the commented line), it didn’t tell the regex engine to suppress the special meaning. If you understood what I’ve explained above, this should come as no surprise. We found a match despite the fact that we used raw strings and so \b's special meaning should have been abandoned. Let’s now explore \b in conjunction with the regex engine. When we do not use a raw string, it prints the character - this is seen by the fact that it deleted the character ( 3) right next to it. We see that when using a raw string, we tell Python to not use \b's special meaning and it prints it literally. Let’s see it in action: > print(r"13\b 5") #I'll refer to this line in the next bullet The duality explored above is the reason why \b is so instructive: it has a special meaning in both the interpreters:įor Python, \b is the backspace character. The same isn’t true for \n which has a special meaning for the Python interpret, but not for the regex engine. What you’re doing when you’re using raw strings is telling the first layer - the Python interpret - to not use the special meaning of the characters.Īs it happens, \w doesn’t have a special meaning to the Python interpreter (it does to the regex engine), so when you use \w and tell Python to ignore its special meaning, Python doesn’t even know what you’re talking about. To repeat the point: the regex engine sees the same thing. That’s because after the Python interpret is done with these strings, they are indeed the same: > print(r"", "") This happens because the regex engine - the second layer mentioned above, receives as input the same thing, whether you use r"" or "". If you were to run findall("", s) you’d find the same result. As you observed \w didn’t lose its special meaning despite the use of a raw string. It matched every letter, and it did so because of \w. We’ll use s to experiment with the pattern and variations of it. We’ll limit our experimentations to re.findall. Let’s explore the example you asked about. And just like Python, some symbols in regex have special meanings: \w, \b and \d to name a few. This language, just like the Python interpreter, reads strings and interprets them. You can think of regular expressions as a language within a language - more specifically, as a language within Python. When we enter the regex world, there is an additional layer, that of regular expressions. This is the first layer that Han mentioned. That’s why we get the behavior we saw above and I repeat below. When we “raw it” we’re telling Python to interpret it literally instead of with its special meaning. What we’re seeing here is Python’s interpreter parsing the inputs and modifying them according to certain rules.įor Python’s interpreter, \n is a special character. In the second print call, we got the same result both times. Notice how in the first print call, it first printed \n and then it printed an actual new line. Let’s begin by printing some stuff and seeing what happens: > print(r"\n", "\n")
0 kommentar(er)
