import re\n<\/pre><\/strong>\n<\/div><\/div>\n\n\n\nTo build a regular expression, the user may use metacharacters<\/span><\/strong>, special sequences<\/span><\/strong>, <\/span><\/strong>and sets<\/span><\/strong>.<\/p>\n\n\n\n
\n\n\n\nMetacharacters<\/strong><\/h2>\n\n\n\nThe metacharacters <\/span><\/strong>are special characters used in building the Regular Expression In Python which has specific meanings<\/span><\/strong> in it. Some of the commonly used metacharacters are:<\/p>\n\n\n\n
\n\n\n\n| Metacharacter<\/th> | Description<\/th> | Example<\/th><\/tr><\/thead> |
|---|
[]<\/span><\/strong><\/td>| A condition can be provided to specify the required set of characters.<\/td> | [a-j], [0-5]<\/span><\/strong><\/td><\/tr>\\<\/strong> <\/span><\/td>| This specifies the usage of escape sequence characters like special sequences.<\/td> | \u201c\\d\u201d<\/span><\/strong><\/td><\/tr>.<\/span><\/strong><\/td>| Specifies any number of characters present between two strings or a set of strings.<\/td> | py…n<\/span><\/strong><\/td><\/tr>^<\/span><\/strong><\/td>| This should be placed before the string or any condition to specify that the result must return the string beginning with the given string.<\/td> | ^the<\/span><\/strong><\/td><\/tr>$<\/span><\/strong><\/td>| This should be placed at the end of the string or condition to specify that the result must return the string ending with the given string.<\/td> | python$<\/span><\/strong><\/td><\/tr>*<\/span><\/strong><\/td>| This should be placed at the end of the given pattern. This specifies that the result must have zero or more occurrences of the given pattern. <\/td> | \u201coo*\u201d<\/span><\/strong><\/td><\/tr>+<\/span><\/strong><\/td>| This should be placed at the end of the given pattern. This specifies that the result must have at least one or more occurrences of the given pattern.<\/td> | \u201coo+\u201d<\/span><\/strong><\/td><\/tr>{}<\/span><\/strong><\/td>| The exact number of required occurrences must be mentioned inside the brackets. <\/td> | \u201coo{1}\u201d<\/span><\/strong><\/td><\/tr>|<\/span><\/strong><\/td>| Two patterns or string will be given. It will check either one among them is present or not. <\/td> | practice | study<\/span><\/strong><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nExample1<\/h3>import re\ntxt = \"Learning python is easy\"\nx = re.findall(\"^Learning.*easy$\", txt)\nprint(x)\n<\/pre><\/strong>\n<\/div>Output<\/h3>['Learning python is easy']<\/pre><\/strong><\/div><\/div>\n\n\n\nExample2<\/h3>import re\ntxt = \"Learning python is easy\"\nx = re.findall(\"py...n\", txt)\nprint(x)\n<\/pre><\/strong>\n<\/div>Output<\/h3>['python']<\/pre><\/strong><\/div><\/div>\n\n\n\nSpecial sequences<\/strong><\/h2>\n\n\n\n
\n\n\n\nThe special sequences are like escape sequences<\/span><\/strong>. They are followed by a character after \\<\/span><\/strong>. Some of the commonly used special sequences are:<\/p>\n\n\n\n
\n\n\n\n- \\A<\/strong> <\/span>\u2013 It is placed before the required string to be searched. It returns the matched string.<\/strong> Example: \\AHello<\/li>
- \\b<\/span><\/strong> \u2013 This is placed before the beginning of the pattern or at the end of the pattern. It returns if the given pattern is found in the beginning or at the end. Example: h\u201d\\bello\u201d \u2013 searches if ello pattern is found at the beginning of any word.<\/strong> h\u201dello\\b\u201d \u2013 searches if ello pattern is found at the end of any word.<\/li>
- \\B<\/span><\/strong> \u2013 This is the exact opposite of \\b. It returns only the strings when the pattern is not in the beginning or at the end.<\/li>
- \\d<\/span><\/strong> \u2013 This can be used to find whether any numbers are present in the given string.<\/li>
- \\D<\/span><\/strong> \u2013 Exact opposite of \\d. It returns the strings given in the input that does not have any numbers.<\/li><\/ul>\n\n\n\n
\n\n\n\nExample1<\/h3>import re\ntest_string= \"Hello world\"\nx = re.findall(\"\\AHello\", test_string)\nprint(x)\n<\/pre><\/strong>\n<\/div>Output<\/h3>['Hello']<\/pre><\/strong><\/div><\/div>\n\n\n\nExample2<\/h3>import re\ntest_string= \"Hello world\"\nx = re.findall(r\"ello\\b\", test_string)\nprint(x)\n<\/pre><\/strong>\n<\/div>Output<\/h3>['ello']<\/pre><\/strong><\/div><\/div>\n\n\n\nSets<\/h2>\n\n\n\n
\n\n\n\nThe sets are always represented by [] <\/span><\/strong>brackets. The sets are special characters<\/span><\/strong> placed inside the brackets in Regular Expression In Python. Some of the common usages of sets are:<\/p>\n\n\n\n
\n\n\n\n- [xyz]<\/strong> <\/span>\u2013 If any of the characters specified in the sets are matched, then it returns the list of matched characters. <\/li>
- [a-j]<\/strong> <\/span>– If any of the characters specified in the sets are matched, then it returns the list of matched characters in alphabetical order.<\/li>
- [^xyz]<\/span><\/strong> – Except the characters specified in the sets other characters are returned.<\/li>
- [123] <\/span><\/strong>– If any of the numbers specified in the sets are matched, then it returns the list of matched numbers.<\/li>
- [0-9]<\/span><\/strong> – If any of the numbers specified in the sets are matched, then it returns the list of matched numbers in order.<\/li>
- [0-4][0-4]<\/span><\/strong> \u2013 This is used for finding two-digit numbers i.e. it returns the number between 00 and 44.<\/li>
- [*+] <\/span><\/strong>\u2013 The special characters which are specified in the sets are matched, then it returns the list of matched characters.<\/li><\/ul>\n\n\n\n
Example1<\/h3>import re\ntxt = \"Happy learning...\"\nx = re.findall(\"[hpyz]\", txt)\nprint(x)\n<\/pre><\/strong>\n<\/div>Output<\/h3>['p', 'p', 'y']<\/pre><\/strong><\/div><\/div>\n\n\n\nExample2<\/h3>import re\ntxt = \"Happy learning...\"\nx = re.findall(\"[...]\", txt)\nprint(x)\n<\/pre><\/strong>\n<\/div>Output<\/h3>['.', '.', '.']<\/pre><\/strong><\/div><\/div>\n\n\n\nFuntions<\/strong><\/h2>\n\n\n\n
\n\n\n\nThe regex expression mainly uses 4 functions. They are:<\/p>\n\n\n\n - findall()<\/span><\/strong><\/li>
- search()<\/span><\/strong><\/li>
- split()<\/span><\/strong><\/li>
- sub()<\/span><\/strong><\/li><\/ul>\n\n\n\n
\n\n\n\nfindall()<\/strong><\/h2>\n\n\n\n
\n\n\n\nThe findall()<\/span><\/strong> method is used to find all the matches and returns it in the form of a list.<\/p>\n\n\n\nExample<\/h3>import re\ntxt = \"Happy learning...\"\nx = re.findall(\"earn\", txt)\nprint(x)\n<\/pre><\/strong>\n<\/div>Output<\/h3>['earn']<\/pre><\/strong><\/div><\/div>\n\n\n\n
\n\n\n\nsearch<\/strong>()<\/strong><\/h2>\n\n\n\n
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