Introduce to string type
ASCII is a sample form of Unicode text, but many text may be not non-English-text source.File working in two modes are text and bytes ,We need to understand differnt of String of object type in Python3.X and Python 2.X.
Python3.X :
(1) str : handle text of Unicode form
(2) bytes : handle binary data
(3) bytearray : handle mutable variant of bytes
Python2.x:
(1) str : handle 8-bits text and binary data
(2) unicode : hanlde Unicode text
(3) bytearray : handle mutable variant of bytes. ( support 2.6 or later)
1.String Basics
Everything is string.String can be used to represent informations of all kinds(e.g. profile, song…), these informations can be encoded as text or bytes.
2.String Literals
In python, String function handle various data types.
| quote mark | description |
|---|---|
| single quote | ‘temp’s’ |
| double quote | “temp’s” |
| triple quotes | “”” mutiline… ””” ‘’’mutilne… ‘’’ |
| raw string | r”data” |
| escape sequences | “s\tdat\n” |
| bytes | b’sp\x01’ |
| unicode | u’eggs\u001’ |
Problem 1. single and double-quoted string are the same ?
In python, single- and double-quote characters are interchangeable. string
literals is written enclosed in either two single or two double quotes.
Example:
>>> 'apple',"apple" ('apple', 'apple') >>> 'Tom"s apple',"Tom's apple" //embed a quote ('Tom"s apple', "Tom's apple") >>> 'Tom\'s apple',"Tom\'s apple" //use escape quote ("Tom's apple", "Tom's apple") |
Escape
| Escape | Description |
|---|---|
| \n | Newline |
| \t | tab |
| \xhh | hex value |
| \o | octal value |
| \’ | single quote |
| \” | double quote |
| \\ | backslash(\) |
| \0 | null: binary 0 character |
| \N{id} | Unicode database ID |
| \uhhhh | Unicode character with 16-bit hex value |
| \uhhhhhhhh | Unicode character with 32-bit hex value |
Example:
>>> “abc\ndef\t ghi ” 'abc\ndef\t ghi' >>> print(“abc\ndef\t ghi ”) ’abc def ghi ’ |
Basic Operations
| Operation | Description |
|---|---|
| len(str) | return the length of a string or size of the string in the memory |
| str + str | return concatenate two string to create new string |
| str * n | return adding a string to itself a number of times |
| [start:end] | return slicing the string |
| [start:end:step] | return slicing the string by step |
s = “abcdefghijklmnopqrstuvwxyz”
>>> s = "abcdefghijklmnopqrstuvwxyz" >>> len(s) 26 >>> s+"1234567890" 'abcdefghijklmnopqrstuvwxyz1234567890' >>> s*2 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz' >>> s[0] 'a' >>> s[-2] 'y' #slicing>>> s[0] 'a' >>> s[-1] 'z' >>> s[1:] #get all elements beyond the first 'bcdefghijklmnopqrstuvwxy' >>> s[3:6] 'def' >>> s[:-1] # get all elements unitl the last |
Note: s[0] fetches the string at offset 0 from the left and return “a”;s[-1] gets the string at offset 1 back from the end.
String conversion
In python, if the string looks like number and you want to add a number and the string together. it will happe a error(TypeError) so you need to convert the string to integer.
>>> "30"+1 Traceback (most recent call last): File "<pyshell#79>", line 1, in <module> "30"+1 TypeError: Can't convert 'int' object to str implicitly |
These are String conversion tools
| conversion | Description |
|---|---|
| int(str) | return converted integer |
| int(str, base=10) | return converted integer by base |
| str(obj) | return converted string |
| repr(obj) | return code string, |
| float(text) | return floating-point-number |
| ord(str) | it only convert a single character to integer |
| chr(int) | an integer code convert to the correspanding character |
| bin(int) | return binary |
(1) A number and a string add together, the string is converted to integer.
(2) A number and a string add together, the number is converted to string.
(3) A string looks like a float-point-number, the string is conveted to float.
a = 1, b = ”2”, c = “3.14”
>>> a = 1 >>> b = "2" >>> c = “3.14” >>> a + int(b) # (1) convert to integer 3 >>> str(a) + b # (2) convert to string '12' >>> float(c) 3.14 |
Example :
(1) single character convert to integer code
(2) integer convert to single character
Example:
(1) binary to integer
(2) integer to binary
>>> int('1111',2) 15 >>> bin(15) '0b1111' |
String function
| function | Description |
|---|---|
| capitalize() | retrun the first character of the string is capitalized |
| casefold() | return the string is lowercased |
| center(int width) | |
| encode(encoding=”utf8”) | Return an encoded version of the string as a bytes object. |
| find(str) | return index in the string where substring is found |
| index(str) | like find() |
| isalpha() | return true if all characters are alphabestic in the string |
| isdecimal() | return true if all characters are decimal in the string |
| isdigit() | return true if all characters are digits in the string |
| lower() | like casefold() |
| split() | return a list of the words in the stirng by sep as the delimiter string. |
| zfill(int width) | return the string filled with ‘0’ |
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