09_New_in_Python/05_Match_Placeholder___regex.ipynb

{"cells":[{"cell_type":"code","execution_count":null,"metadata":{"id":"Shqn5p58bY9Z"},"outputs":[],"source":["#check python version\n","import sys\n","print(sys.version)\n","!python3 --version\n","!python --version"]},{"cell_type":"markdown","metadata":{"id":"IFKzDQuXkibM"},"source":["## Placeholder `_`"]},{"cell_type":"markdown","metadata":{"id":"8X-erH5wiy9C"},"source":["The underscore `(_)` is a special character in Python that has various uses. For example, it is commonly used as a placeholder for an unused variable, or to represent the result of the last executed expression when used in the interactive interpreter.\n","\n","Here is an example of how the underscore can be used as a placeholder for an unused variable:"]},{"cell_type":"code","execution_count":null,"metadata":{"id":"DAfvc-FYj7WM"},"outputs":[],"source":["# Assign the value 10 to the variable `x`\n","x = 10\n","\n","# This expression is not assigned to any variable, so the result is discarded\n","# and the underscore is used as a placeholder\n","_ = x * 2\n","\n","# At this point, the value of `x` is still 10, since the underscore is not a\n","# reference to the result of the previous expression\n","print(x)  # Output: 10"]},{"cell_type":"markdown","metadata":{"id":"d4aLR5YCkBXU"},"source":["In the interactive interpreter, the underscore can also be used to access the result of the last executed expression:"]},{"cell_type":"code","execution_count":null,"metadata":{"id":"UYv_eapwkELr"},"outputs":[],"source":["print(2 + 3)\n","print(_ * 5)"]},{"cell_type":"markdown","metadata":{"id":"fd-twxIMkQ8r"},"source":["As you can see in this example, the underscore can be used as a shortcut to refer to the result of the last executed expression, without having to re-enter the entire expression.\n","\n","It's worth noting that using the underscore as a variable name is generally discouraged in Python, since it can be easily confused with the special uses of the character. It's best to use a more descriptive variable name to avoid confusion."]},{"cell_type":"code","execution_count":null,"metadata":{"id":"KtxJfr72jMkO"},"outputs":[],"source":["# This list contains the numbers from 1 to 10\n","numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]\n","\n","# We want to print out each number, but we don't need to do anything with\n","# the loop variable itself, so we use the underscore character (_) as a\n","# placeholder for the loop variable\n","for _ in numbers:\n","  print(_)"]},{"cell_type":"markdown","metadata":{"id":"ez6CVjbxjS4G"},"source":["In this example, we use a for loop to iterate over a list of numbers. We use the `_` character as the loop variable, which means that we don't need to use the loop variable itself for anything other than to indicate that the loop is running. This allows us to simply print out each number in the list without having to worry about doing anything with the loop variable itself.\n","\n","Another common use for the `_` character is as a variable name for a value that you don't intend to use. For example, you might use it when calling a function that returns multiple values, but you're only interested in using one of the values. "]},{"cell_type":"markdown","metadata":{"id":"MIwcD0yQkon6"},"source":["## Match"]},{"cell_type":"code","execution_count":null,"metadata":{"id":"a-cd3sDrdk0p"},"outputs":[],"source":["a = int(input(\"enter your number:\\n\"))\n","match a:\n","    case 0:\n","        print(\"it's zero\")\n","    case _: # we use underscore for default case\n","        print(\"it's not a zero\")"]},{"cell_type":"code","execution_count":null,"metadata":{"id":"Evx9NC7it8dD"},"outputs":[],"source":["x = int(input(\"Enter the value of x: \"))\n","        \n","# x is the variable to match\n","match x:\n","    # if x is 0\n","    case 0:\n","        print(\"x is zero\" )\n","    # case with if-condition\n","    case 1:\n","        print( \"case is one\")\n","    case _: #default case\n","        print(x)"]},{"cell_type":"code","execution_count":null,"metadata":{"id":"jY-5REuwas2a"},"outputs":[],"source":["x = int(input(\"Enter the value of x: \"))\n","# x is the variable to match\n","match x:\n","    # if x is 0\n","    case 0:\n","        print(\"x is zero\")\n","    # case with if-condition\n","    case 4:\n","        print(\"case is 4\")\n","\n","    case _ if x!=90:\n","        print(x, \"is not 90\")\n","    case _ if x!=80:\n","        print(x, \"is not 80\")\n","    case _:\n","        print(x)"]},{"cell_type":"code","execution_count":null,"metadata":{"id":"EcwpG8T3f1Pg"},"outputs":[],"source":["x = int(input(\"Enter a Number: \"))\n","# x is the variable to match\n","match x:\n","    # if x is 0\n","    case 0:\n","        print(\"x is zero\")\n","\n","    # case with if-condition\n","    case 4 if x % 2 == 0:\n","        print(\"x % 2 == 0 and case is 4\")\n","\n","    # Empty case with if-condition\n","    case _ if x < 10:\n","        print(\"x is < 10\")\n","\n","    # default case(will only be matched if the above cases were not matched)\n","    # so it is basically just an else:\n","    case _:\n","        print(x)"]},{"cell_type":"markdown","metadata":{"id":"-ioIDC9HfIXw"},"source":["## `re`"]},{"cell_type":"markdown","metadata":{"id":"7oOkW_2cmq9u"},"source":["The re module in Python is part of the standard library and provides support for regular expressions. Regular expressions are a powerful tool for matching and manipulating strings, and they can be used in a variety of ways in Python.\n","\n","Here is a simple example of how the re module can be used to search for a pattern in a string:"]},{"cell_type":"code","execution_count":null,"metadata":{"id":"ZLYZgAFBmrtL"},"outputs":[],"source":["import re\n","\n","# Define a string to search\n","my_string = \"The quick brown fox jumps over the lazy dog\"\n","\n","# Use the `search` method from the `re` module to find a pattern in the string\n","result = re.search(r\"fox\", my_string)\n","\n","# Print the result\n","print(result)  # Output: <re.Match object; span=(16, 19), match='fox'>"]},{"cell_type":"markdown","metadata":{"id":"b1ozp1Yemv6c"},"source":["In this example, the search method from the `re` module is used to search for the pattern `\"fox\"` in the my_string variable. The `r` prefix before the string indicates that the string is a \"raw string\", which means that backslashes `(\\)` in the string are treated as literal backslashes, rather than as escape characters.\n","\n","If the search method finds a match for the pattern, it returns a Match object that contains information about the match, such as the starting and ending positions of the match within the string. If the search method does not find a match, it returns None.\n","\n","There are many other methods and functions available in the `re` module, including functions for splitting strings, replacing substrings, and more. You can learn more about the re module and how to use it in the Python documentation."]},{"cell_type":"code","execution_count":null,"metadata":{"id":"5L-ztjjeeD6H"},"outputs":[],"source":["import re\n","\n","# Define the regular expression\n","pattern = r\"Hello\"\n","\n","# Define the string to search\n","string = \"Hello, world!\"\n","\n","# Search the string for a match to the pattern\n","match = re.match(pattern, string)\n","\n","# Check if a match was found\n","if match:\n","    print(\"Hello found!\")\n","else:\n","    print(\"Hello not found\")"]},{"cell_type":"markdown","metadata":{"id":"5EUsifRyeY15"},"source":["In this example, the `re.match()` function searches the `string` for the text \"Hello\". If it is found at the beginning of the string, it prints a message saying that \"Hello\" was found. If it is not found, it prints a message saying that \"Hello\" was not found.\n","\n","This example shows how you can use the `re.match()` function to check if a given pattern appears at the beginning of a string. You can modify the regular expression and the string to match whatever pattern you want."]},{"cell_type":"code","execution_count":null,"metadata":{"id":"aVEj6MiIe0V8"},"outputs":[],"source":["import re\n","\n","# Match a phone number with or without a leading \"+\" sign\n","pattern = r\"\\+?\\d{3}-\\d{3}-\\d{4}\"\n","string = \"My phone number is +1-555-555-1234\"\n","match = re.match(pattern, string)\n","if match:\n","    print(f\"Phone number found: {match.group()}\")\n","else:\n","    print(\"Phone number not found\")\n","\n","# Match a date in the format \"YYYY-MM-DD\"\n","pattern = r\"\\d{4}-\\d{2}-\\d{2}\"\n","string = \"Today's date is 2022-12-14\"\n","match = re.match(pattern, string)\n","if match:\n","    print(f\"Date found: {match.group()}\")\n","else:\n","    print(\"Date not found\")\n","\n","# Match an email address\n","pattern = r\"[\\w.-]+@[\\w.-]+\"\n","string = \"My email address is myname@example.com\"\n","match = re.match(pattern, string)\n","if match:\n","    print(f\"Email address found: {match.group()}\")\n","else:\n","    print(\"Email address not found\")"]}],"metadata":{"colab":{"provenance":[]},"kernelspec":{"display_name":"Python 3 (ipykernel)","language":"python","name":"python3"},"language_info":{"codemirror_mode":{"name":"ipython","version":3},"file_extension":".py","mimetype":"text/x-python","name":"python","nbconvert_exporter":"python","pygments_lexer":"ipython3","version":"3.10.5"}},"nbformat":4,"nbformat_minor":0}