{ "cells": [ { "cell_type": "markdown", "id": "e1a268a7", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "# String Processing and Formatting\n", "#### CS 65: Introduction to Computer Science I" ] }, { "cell_type": "markdown", "id": "0696b12b", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Review: Useful string methods we've used\n", "\n", "* `rstrip()` - strip out newlines/whitespace at the end of a string\n", "* `split()` - split a string into a list of strings based on a delimeter\n", "* `index()` - find a substring inside a string\n", "* `count()` - count the number of times a substring appears in a string" ] }, { "cell_type": "markdown", "id": "cf4d0ba5", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Other string methods to know about\n", "It's always good to be aware of a whole bunch of string methods - they can come in very handy.\n", "\n", "See https://www.w3schools.com/python/python_ref_string.asp\n", "\n", "Here's a sample:\n" ] }, { "cell_type": "code", "execution_count": 1, "id": "c0845047", "metadata": { "slideshow": { "slide_type": "fragment" } }, "outputs": [ { "data": { "text/plain": [ "False" ] }, "execution_count": 1, "metadata": {}, "output_type": "execute_result" } ], "source": [ "name = \"Eric\"\n", "#check if all the characters are lowercase\n", "name.islower()" ] }, { "cell_type": "code", "execution_count": 2, "id": "7c121bab", "metadata": { "slideshow": { "slide_type": "fragment" } }, "outputs": [ { "data": { "text/plain": [ "'eric'" ] }, "execution_count": 2, "metadata": {}, "output_type": "execute_result" } ], "source": [ "lowercase_name = name.lower()\n", "lowercase_name" ] }, { "cell_type": "code", "execution_count": 3, "id": "0007d7f2", "metadata": { "slideshow": { "slide_type": "fragment" } }, "outputs": [ { "data": { "text/plain": [ "True" ] }, "execution_count": 3, "metadata": {}, "output_type": "execute_result" } ], "source": [ "name1 = \"eric\"\n", "name2 = \"Titus\"\n", "name1.lower() < name2.lower()" ] }, { "cell_type": "code", "execution_count": 4, "id": "4b1a7809", "metadata": { "slideshow": { "slide_type": "fragment" } }, "outputs": [ { "data": { "text/plain": [ "'Eric'" ] }, "execution_count": 4, "metadata": {}, "output_type": "execute_result" } ], "source": [ "name1 = \"eric\"\n", "name1.capitalize()" ] }, { "cell_type": "markdown", "id": "dcdea34d", "metadata": { "slideshow": { "slide_type": "subslide" } }, "source": [ "### Here's a potential problem with user input:" ] }, { "cell_type": "code", "execution_count": 5, "id": "f90bfacb", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Enter a number: ten\n" ] }, { "ename": "ValueError", "evalue": "could not convert string to float: 'ten'", "output_type": "error", "traceback": [ "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[0;31mValueError\u001b[0m Traceback (most recent call last)", "\u001b[0;32m\u001b[0m in \u001b[0;36m\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0muser_input\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mfloat\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0minput\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"Enter a number: \"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m 2\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"Your number divided by 2 is\"\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0muser_input\u001b[0m\u001b[0;34m/\u001b[0m\u001b[0;36m2\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n", "\u001b[0;31mValueError\u001b[0m: could not convert string to float: 'ten'" ] } ], "source": [ "user_input = float(input(\"Enter a number: \"))\n", "print(\"Your number divided by 2 is\",user_input/2)" ] }, { "cell_type": "markdown", "id": "f57ddada", "metadata": { "slideshow": { "slide_type": "fragment" } }, "source": [ "Here's a fix" ] }, { "cell_type": "code", "execution_count": 6, "id": "1774a993", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Enter a number: ten\n", "That's not a number!\n" ] } ], "source": [ "user_input = input(\"Enter a number: \")\n", "if user_input.isnumeric():\n", " user_input = float(user_input)\n", " print(\"Your number divided by 2 is\",user_input/2)\n", "else:\n", " print(\"That's not a number!\")" ] }, { "cell_type": "markdown", "id": "29e5a4a4", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Some formatting annoyances\n", "\n", "Perhaps you have tried to do something like this, and you end up with a space between the $ and the number that you don't want." ] }, { "cell_type": "code", "execution_count": 7, "id": "d8903ab6", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Employee 123 made $ 980.543 this period.\n" ] } ], "source": [ "employee_num = 123\n", "pay = 980.543\n", "print(\"Employee\",employee_num,\"made $\",pay,\"this period.\")" ] }, { "cell_type": "markdown", "id": "ede8d0ef", "metadata": { "slideshow": { "slide_type": "fragment" } }, "source": [ "## The `format()` method\n", "\n", "The `format()` method allows you to substitute values into placeholders within a string." ] }, { "cell_type": "code", "execution_count": 8, "id": "216db29a", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Employee 123 made $980.543 this pay period.\n" ] } ], "source": [ "employee_num = 123\n", "pay = 980.543\n", "pay_message = \"Employee {n} made ${p} this pay period.\"\n", "print( pay_message.format(n=employee_num, p=pay) )" ] }, { "cell_type": "markdown", "id": "bb89d3bd", "metadata": { "slideshow": { "slide_type": "fragment" } }, "source": [ "You can even do it in one step:" ] }, { "cell_type": "code", "execution_count": 9, "id": "d4ad89c7", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Employee 123 made $980.543 this pay period.\n" ] } ], "source": [ "employee_num = 123\n", "pay = 980.543\n", "print( \"Employee {n} made ${p} this pay period.\".format(n=employee_num, p=pay) )" ] }, { "cell_type": "markdown", "id": "140783e6", "metadata": { "slideshow": { "slide_type": "fragment" } }, "source": [ "You can even add formatting information to the placeholders for things like how to format numbers.\n", "\n", "In this example `\":.2f\"` means format as a floating-point number with 2 places to the right of the decimal point." ] }, { "cell_type": "code", "execution_count": 10, "id": "1bb729e3", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Employee 123 made $980.54 this pay period.\n" ] } ], "source": [ "employee_num = 123\n", "pay = 980.543\n", "print( \"Employee {n} made ${p:.2f} this pay period.\".format(n=employee_num, p=pay) )" ] }, { "cell_type": "markdown", "id": "339115bc", "metadata": { "slideshow": { "slide_type": "fragment" } }, "source": [ "`\":.0%\"` means format as a percentage with 0 decimal places" ] }, { "cell_type": "code", "execution_count": 11, "id": "12261984", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Eric earned a 90% on the test\n" ] } ], "source": [ "\n", "print(\"{name} earned a {perc_grade:.0%} on the test\".format(name=\"Eric\",perc_grade=.897))" ] }, { "cell_type": "markdown", "id": "e92d2138", "metadata": { "slideshow": { "slide_type": "subslide" } }, "source": [ "### How can you know how to use all of these things?\n", "\n", "You just have to know it's a thing, and look it up when you need to use it.\n", "\n", "https://docs.python.org/3/library/string.html#formatstrings\n", "\n", "https://www.w3schools.com/python/ref_string_format.asp" ] }, { "cell_type": "markdown", "id": "f1069ee6", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Review: Character representation\n", "\n", "Every text character is represented by a numerical code in your computer's memory. \n", "\n", "They came up with in the 1960's as part of the ASCII standard (https://en.wikipedia.org/wiki/ASCII)\n", "\n", "Here's some examples\n", "\n", "\n", "\n", " \n", " \n", "
\n", " \n", " \n", " \n", " \n", " \n", " \n", " \n", "
code character
33 !
34 \"
35 #
36 $
37 %
\n", " 		\n", " \n", " \n", " \n", " \n", " \n", " \n", " \n", "
code character
65 A
66 B
67 C
68 D
69 E
\n", " 		\n", " \n", " \n", " \n", " \n", " \n", " \n", " \n", "
code character
97 a
98 b
99 c
100 d
101 e
\n", " \n", "
\n", " \n", "You can use the built-in `ord()` function to look up the code for any given character. Use `chr()` to do the opposite." ] }, { "cell_type": "code", "execution_count": 12, "id": "a28db44b", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "65" ] }, "execution_count": 12, "metadata": {}, "output_type": "execute_result" } ], "source": [ "ord(\"A\")" ] }, { "cell_type": "code", "execution_count": 13, "id": "f6a45e70", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'A'" ] }, "execution_count": 13, "metadata": {}, "output_type": "execute_result" } ], "source": [ "chr(65)" ] }, { "cell_type": "markdown", "id": "4b923a5e", "metadata": {}, "source": [ "In the lab, we are going to use the functions to do some encryption on strings." ] } ], "metadata": { "celltoolbar": "Slideshow", "kernelspec": { "display_name": "Python 3", "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": "3.8.8" } }, "nbformat": 4, "nbformat_minor": 5 }