![]() There are some more rarely used variations of s.find(): s.find(x, start_index) - which begins the search at the given index instead of at 0 s.rfind(x) does the search right-to-left from the end of the string. Use s.find() to compute the index where a substring first appears. S.find(x) - searches s left to right, returns int index where string x appears, or -1 if not found. S.endswith(x) - True if s ends with string x S.startswith(x) - True if s start with string x These are convenient when you need to check for something at an end, e.g. These convenient functions return a boolean True/False depending on what appears at one end of a string. In some alphabets, there are chars which are alphabetic, but which do not have upper/lower versions. Unicode aside: In the roman a-z alphabet, all alphabetic chars have upper/lower versions. Then there are all the other miscellaneous characters like '$' '^' '> 'a'.isalpha() Alphabetic chars are further divided into upper and lowercase versions (the details depend on the particular unicode alphabet).ĭigit chars - e.g. The characters that make up a string can be divided into several categories or "character classes":Īlphabetic chars - e.g. > '' in 'abcd' # empty string in always True > 'aa' in 'iiaaii' # test string can be any length In this and other string comparisons, characters much match exactly, so 'a' matches 'a', but does not match 'A'.(Mnemonic: this is the same word "in" as used in the for-loop.) ![]() The in operator checks, True or False, if something appears anywhere in a string. TypeError: can only concatenate str (not "int") to str Call the function str() function to make a string out of an int, then concatenation works. (See the working with immutable below.)Ĭoncatenate + only works with 2 or more strings, not for example to concatenate a string and an int. This creates new strings to represent the result, leaving the original strings unchanged. The + operator combines (aka "concatenates") two strings to make a bigger string. TypeError: 'str' object does not support item assignment + below), leaving the original strings unchanged. Code to compute a different string always creates a new string in memory to represent the result (e.g. Strings are immutable, so they cannot be changed once created. ValueError: invalid literal for int() with base 10: 'xx1234'Ĭhars are accessed with zero-based indexing with square brackets, so the first chars is index 0, the next index 1, and the last char is at index len-1.Īccessing a too large index number is an error. > int('xx1234') # fails due to extra chars Going the other direction, the formal name of the integer type is "int", and the int() function takes in a value and tries to convert it to be an int value: Looking carefully at the values, 123 is a number, while '123' is a string length-3, made of the three chars '1' '2' and '3'. Here is an example this code computes the str form of the number 123: The str() function serves to convert many values to a string form. The formal name of the string type is "str". The len() function in Python is omnipresent - it's used to retrieve the length of every data type, with string just a first example. It is valid to have a string of zero characters, written just as '', called the "empty string". The len() function returns the length of a string, the number of chars in it. ![]() See the unicode section below for more information. Python strings are written between single quote marks like 'Hello' or alternately they can be written in double quote marks like "There".Įach character in a string is drawn from the unicode character set, which includes the "characters" or pretty much every language on earth, plus many emojis. Text is central to many compautions - urls, chat messages, the underlying HTML code that makes up web pages. A Python string, like 'Hello' stores text as a sequence of individual characters.
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