Python functions are first-class objects, and for this reason, they provide good functionality to developers, one of which is passing functions as arguments, which we will learn how to do in this article.<\/p>\n
Suppose we have a list of strings representing the names of fruits:<\/p>\n
>>> fruits = ['kumquat', 'cherimoya', 'Loquat', 'longan', 'jujube']<\/pre>\n<\/div>\nIf we want to sort this list alphabetically, we can pass it to the built-in sort function:<\/p>\n
\n>>> sorted(fruits)\r\n\r\n['Loquat', 'cherimoya', 'jujube', 'kumquat', 'longan']<\/pre>\n<\/div>\nAs you can see, the sorting is not strictly alphabetical because when Python<\/strong> sorts strings, it puts all uppercase letters before all lowercase letters due to the structure of the Unicode and ASCII encoding<\/a> systems.\u00a0We can solve this problem by providing a key argument to the built-in sorter function.<\/p>\n
\n>>> help(sorted)\r\n\r\nsorted(iterable, \/, *, key=None, reverse=False)\r\n\r\n...<\/pre>\n<\/div>\nThis key argument should be a function with each item in the fruit list to sort all the elements according to what we want.<\/p>\n
In the example above, we can create a function that lowers the letters of any given string so that the sorting process is based on lowercase letters.<\/p>\n
\n>>> def lowercase(string):\r\n\r\n...\u00a0\u00a0\u00a0\u00a0 return string.lower()\r\n\r\n...<\/pre>\n<\/div>\nTo sort by lowercase strings, we call the sorter with a key argument that points to this lowercase function:<\/h4>\n
\n>>> sorted(fruits, key=lowercase)\r\n\r\n['cherimoya', 'jujube', 'kumquat', 'longan', 'Loquat']<\/pre>\n<\/div>\nThis will correctly sort our list of strings alphabetically while preserving the original letter combinations.<\/p>\n
Note that when we call the sorter function, we didn’t put the parentheses (()) after the lowercase letters to call it, and we used the following calling pattern:<\/p>\n
\n>>> lowercase('X')\r\n\r\n'x'<\/pre>\n<\/div>\nAs you can see, we have not reduced the characters of the string in any way, and we only mentioned the lowercase letters:<\/p>\n
\n>>> lowercase\r\n\r\n<function lowercase at 0x7fc8a3fc09d0><\/pre>\n<\/div>\nWe passed the lowercase function object to the sorter function via its key argument:<\/span><\/h3>\n
\n>>> sorted(fruits, key=lowercase)<\/pre>\n<\/div>\nThe above example shows that Python allows us to pass functions as arguments to other functions. o that the sorter function can repeatedly call itself on each unique item in the lowercase fruit list, optimizing the sorting process by using the return value as a comparison key. To better understand the issue, let us refer to other models.<\/p>\n
Another example of assigning a function to a variable<\/a> as an object<\/span><\/h2>\n
In the following example, a function is assigned to a variable; the procedure is not called in the above allocation process. Instead, the object of the mentioned function is received by shoutout and delivered to the yell variable.
\nFinally, the input parameter is entered in the yell print command. Receives a pass to the function to print the word hello in capital letters.<\/p>\n\n# Python program to illustrate functions\r\n\r\n# can be treated as objects\r\n\r\ndef shout(text):\r\n\r\nreturn text.upper()\r\n\r\n\r\n\r\n\r\nprint(shout('Hello'))\r\n\r\n\r\n\r\n\r\nyell = shout\r\n\r\n\r\n\r\n\r\nprint(yell('Hello'))<\/pre>\n<\/div>\nHigher Order Functions<\/span><\/h2>\n
Since functions are objects, we can pass them as arguments to other functions. Functions that can accept other functions as arguments are called higher-order functions. In the following example, a function called greet is created, which receives a function as an argument.<\/p>\n
\n# Python program to illustrate functions\r\n\r\n# can be passed as arguments to other functions\r\n\r\ndef shout(text):\r\n\r\nreturn text.upper()\r\n\r\n\r\n\r\n\r\ndef whisper(text):\r\n\r\nreturn text.lower()\r\n\r\n\r\n\r\n\r\ndef greet(func):\r\n\r\n# storing the function in a variable\r\n\r\ngreeting = func(\"Hi, I am created by a function passed as an argument.\")\r\n\r\nprint(greeting)\r\n\r\n\r\n\r\n\r\ngreet(shout)\r\n\r\ngreet(whisper)<\/pre>\n<\/div>\nIn the code above, the shout function is defined, which receives a string variable as input, converts it to uppercase letters, and returns it as the function’s return value.<\/p>\n
Next, a second function called whisper is defined, which receives a string variable but converts it to lowercase letters and returns it as the function’s return value.<\/p>\n