We have already seen some basics of strings in a previous post. Although, here we go in more detail about strings in Python.
Strings are amongst the most popular types in Python. We can create them simply by enclosing characters in quotes. Python treats single quotes the same as double quotes. You can declare string simply as var1=“Hello World”. Moreover, Python also does not support a character type; these are treated as strings of length one, thus also considered a substring.
To access substrings, use the square brackets for slicing along with the index or indices to obtain your substring. For example −
In Python, strings come with so many special operators which are helpful in many ways to decrease the number of lines of codes. We will some of the important operators.
Special String Operators in Python:
|+||Concatenation – Adds values on either side of the operator||a + b will give HelloPython|
|*||Repetition – Creates new strings, concatenating multiple copies of the same string||a*2 will give -HelloHello|
|||Slice – Gives the character from the given index||a will give e|
|[ : ]||Range Slice – Gives the characters from the given range||a[1:4] will give ell|
|in||Membership – Returns true if a character exists in the given string||H in a will give 1|
|not in||Membership – Returns true if a character does not exist in the given string||M not in a will give 1|
|r/R||Raw String – Suppresses actual meaning of Escape characters. The syntax for raw strings is exactly the same as for normal strings with the exception of the raw string operator, the letter “r,” which precedes the quotation marks. The “r” can be lowercase (r) or uppercase (R) and must be placed immediately preceding the first quote mark.||print r’\n’ prints \n and print R’\n’prints \n|
|%||Format – Performs String formatting||see later|
Just like special operators, there are also various formatting operators in python.
One of Python’s coolest features is the string format operator %. This operator is unique to strings and makes up for the pack of having functions from C’s printf() family. Following is a simple example −
|%s||string conversion via str() prior to formatting|
|%i||signed decimal integer|
|%d||signed decimal integer|
|%u||unsigned decimal integer|
|%x||hexadecimal integer (lowercase letters)|
|%X||hexadecimal integer (UPPERcase letters)|
|%e||exponential notation (with lowercase ‘e’)|
|%E||exponential notation (with UPPERcase ‘E’)|
|%f||floating point real number|
|%g||the shorter of %f and %e|
|%G||the shorter of %f and %E|
|*||argument specifies width or precision|
|+||display the sign|
|leave a blank space before a positive number|
|#||add the octal leading zero ( ‘0’ ) or hexadecimal leading ‘0x’ or ‘0X’, depending on whether ‘x’ or ‘X’ were used.|
|0||pad from left with zeros (instead of spaces)|
|%||‘%%’ leaves you with a single literal ‘%’|
|(var)||mapping variable (dictionary arguments)|
|m.n.||m is the minimum total width and n is the number of digits to display after the decimal point (if appl.)|
There are also many built-in methods that strings provide in Python. I will list out all of them first and then take examples of some of the important methods that are used frequently.
Built-in Methods of String
Capitalizes first letter of string
Returns a space-padded string with the original string centered to a total of width columns.
count(str, beg= 0,end=len(string))
Counts how many times str occurs in string or in a substring of string if starting index beg and ending index end are given.
Decodes the string using the codec registered for encoding. encoding defaults to the default string encoding.
Returns encoded string version of string; on error, default is to raise a ValueError unless errors is given with ‘ignore’ or ‘replace’.
endswith(suffix, beg=0, end=len(string))
Determines if string or a substring of string (if starting index beg and ending index end are given) ends with suffix; returns true if so and false otherwise.
Expands tabs in string to multiple spaces; defaults to 8 spaces per tab if tabsize not provided.
find(str, beg=0 end=len(string))
Determine if str occurs in string or in a substring of string if starting index beg and ending index end are given returns index if found and -1 otherwise.
index(str, beg=0, end=len(string))
Same as find(), but raises an exception if str not found.
Returns true if string has at least 1 character and all characters are alphanumeric and false otherwise.
Returns true if string has at least 1 character and all characters are alphabetic and false otherwise.
Returns true if string contains only digits and false otherwise.
Returns true if string has at least 1 cased character and all cased characters are in lowercase and false otherwise.
Returns true if a unicode string contains only numeric characters and false otherwise.
Returns true if string contains only whitespace characters and false otherwise.
Returns true if string is properly “titlecased” and false otherwise.
Returns true if string has at least one cased character and all cased characters are in uppercase and false otherwise.
Merges (concatenates) the string representations of elements in sequence seq into a string, with separator string.
Returns the length of the string
Returns a space-padded string with the original string left-justified to a total of width columns.
Converts all uppercase letters in string to lowercase.
Removes all leading whitespace in string.
Returns a translation table to be used in translate function.
Returns the max alphabetical character from the string str.
Returns the min alphabetical character from the string str.
replace(old, new [, max])
Replaces all occurrences of old in string with new or at most max occurrences if max given.
Same as find(), but search backwards in string.
rindex( str, beg=0, end=len(string))
Same as index(), but search backwards in string.
Returns a space-padded string with the original string right-justified to a total of width columns.
Removes all trailing whitespace of string.
Splits string according to delimiter str (space if not provided) and returns list of substrings; split into at most num substrings if given.
Splits string at all (or num) NEWLINEs and returns a list of each line with NEWLINEs removed.
Determines if string or a substring of string (if starting index beg and ending index end are given) starts with substring str; returns true if so and false otherwise.
Performs both lstrip() and rstrip() on string
Inverts case for all letters in string.
Returns “titlecased” version of string, that is, all words begin with uppercase and the rest are lowercase.
Translates string according to translation table str(256 chars), removing those in the del string.
Converts lowercase letters in string to uppercase.
Returns original string leftpadded with zeros to a total of width characters; intended for numbers, zfill() retains any sign given (less one zero).
Returns true if a unicode string contains only decimal characters and false otherwise.