1.10 Python Strings
Accessing Values in Strings
নিচের কোডটি লক্ষ্য করি,
#!/usr/bin/python var1 = 'Hello World!' var2 = "Python Programming" print "var1[0]: ", var1[0] print "var2[1:5]: ", var2[1:5]
উপরের কোডটি রান করালে নিচের ফলাফল প্রিন্ট হবে।
var1[0]: H var2[1:5]: ytho
Updating Strings
অন্য একটি স্ট্রিং এর সাথে কোন ভেরিয়েবল এসাইন করে একটি স্ট্রিং কে আপডেট করা যায়। যেমনঃ
#!/usr/bin/python var1 = 'Hello World!' print "Updated String :- ", var1[:6] + 'Python'
উপরের কোডটি রান করালে নিচের ফলাফল আসবে।
Updated String :- Hello Python
Escape Characters
নিচের টেবিলে কিছু Escape Characters দেয়া হল, যেগুলো কখনো প্রোগ্রাম রেসাল্টের প্রিন্টে আসে না। এধরনের Escape Characters ব্যবহার করতে কিছু Backslash notation ব্যবহৃত হয়।
| Backslash notation |
Hexadecimal character |
Description |
| \a | 0x07 | Bell or alert |
| \b | 0x08 | Backspace |
| \cx | Control-x | |
| \C-x | Control-x | |
| \e | 0x1b | Escape |
| \f | 0x0c | Formfeed |
| \M-\C-x | Meta-Control-x | |
| \n | 0x0a | Newline |
| \nnn | Octal notation, where n is in the range 0.7 | |
| \r | 0x0d | Carriage return |
| \s | 0x20 | Space |
| \t | 0x09 | Tab |
| \v | 0x0b | Vertical tab |
| \x | Character x | |
| \xnn | Hexadecimal notation, where n is in the range 0.9, a.f, or A.F |
Triple Quotes
Python এ triple quote এর সাহায্যে একাধিক লাইনের স্টেটমেন্ট লেখা হয়। triple quote বোঝাতে তিনটি সিঙ্গেল (’’’) অথবা ডাবল কোটিং (”””) চিহ্ন ব্যবহৃত হয়।
#!/usr/bin/python para_str = """this is a long string that is made up of several lines and non-printable characters such as TAB ( \t ) and they will show up that way when displayed. NEWLINEs within the string, whether explicitly given like this within the brackets [ \n ], or just a NEWLINE within the variable assignment will also show up. """ print para_str
উপরের কোডটির রেসাল্ট হবে,
this is a long string that is made up of several lines and non-printable characters such as TAB ( ) and they will show up that way when displayed. NEWLINEs within the string, whether explicitly given like this within the brackets [ ], or just a NEWLINE within the variable assignment will also show up.
Raw strings ব্যবহার করলে backslash character গুলোর ব্যবহার হয় না। যেমন,
#!/usr/bin/python print r'C:\\nowhere'
উপরের কোডটি চালালে নিচের রেসাল্ট আসবে।
C:\\nowhere
Unicode String
Normal strings গুলোকে Python 8-bit ASCII ফরম্যাটে স্টোর করে, কিন্তু Unicode strings গুলো 16-bit Unicode আকারে স্টোর হয়। এর ফলে একটু ভিন্ন ধরনের ক্যারেকটার ব্যবহার করা সম্ভব হয়।
#!/usr/bin/python print u'Hello, world!'
উপরের কোডটি নিচের রেসাল্ট দিবে।
Hello, world!
Unicode strings এ prefix u ব্যবহৃত হয়, আর raw strings এ prefix r এর ব্যবহার হয়।
Built-in String Methods
Python নিচের বিল্ট−ইন মেথোডগুলোর সাহায্যে স্ট্রিং গুলোকে প্রভাবিত করতে পারে।
| SN | Methods with Description |
| 1 | capitalize() Capitalizes first letter of string |
| 2 | center(width, fillchar) Returns a space-padded string with the original string centered to a total of width columns. |
| 3 | 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. |
| 4 | decode(encoding='UTF-8',errors='strict') Decodes the string using the codec registered for encoding. encoding defaults to the default string encoding. |
| 5 | encode(encoding='UTF-8',errors='strict') Returns encoded string version of string; on error, default is to raise a ValueError unless errors is given with 'ignore' or 'replace'. |
| 6 | 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. |
| 7 | expandtabs(tabsize=8) Expands tabs in string to multiple spaces; defaults to 8 spaces per tab if tabsize not provided. |
| 8 | 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. |
| 9 | index(str, beg=0, end=len(string)) Same as find(), but raises an exception if str not found. |
| 10 | isalnum() Returns true if string has at least 1 character and all characters are alphanumeric and false otherwise. |
| 11 | isalpha() Returns true if string has at least 1 character and all characters are alphabetic and false otherwise. |
| 12 | isdigit() Returns true if string contains only digits and false otherwise. |
| 13 | islower() Returns true if string has at least 1 cased character and all cased characters are in lowercase and false otherwise. |
| 14 | isnumeric() Returns true if a unicode string contains only numeric characters and false otherwise. |
| 15 | isspace() Returns true if string contains only whitespace characters and false otherwise. |
| 16 | istitle() Returns true if string is properly "titlecased" and false otherwise. |
| 17 | isupper() Returns true if string has at least one cased character and all cased characters are in uppercase and false otherwise. |
| 18 | join(seq) Merges (concatenates) the string representations of elements in sequence seq into a string, with separator string. |
| 19 | len(string) Returns the length of the string |
| 20 | ljust(width[, fillchar]) Returns a space-padded string with the original string left-justified to a total of width columns. |
| 21 | lower() Converts all uppercase letters in string to lowercase. |
| 22 | lstrip() Removes all leading whitespace in string. |
| 23 | maketrans() Returns a translation table to be used in translate function. |
| 24 | max(str) Returns the max alphabetical character from the string str. |
| 25 | min(str) Returns the min alphabetical character from the string str. |
| 26 | replace(old, new [, max]) Replaces all occurrences of old in string with new or at most max occurrences if max given. |
| 27 | rfind(str, beg=0,end=len(string)) Same as find(), but search backwards in string. |
| 28 | rindex( str, beg=0, end=len(string)) Same as index(), but search backwards in string. |
| 29 | rjust(width,[, fillchar]) Returns a space-padded string with the original string right-justified to a total of width columns. |
| 30 | rstrip() Removes all trailing whitespace of string. |
| 31 | split(str="", num=string.count(str)) Splits string according to delimiter str (space if not provided) and returns list of substrings; split into at most num substrings if given. |
| 32 | splitlines( num=string.count('\n')) Splits string at all (or num) NEWLINEs and returns a list of each line with NEWLINEs removed. |
| 33 | startswith(str, beg=0,end=len(string)) 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. |
| 34 | strip([chars]) Performs both lstrip() and rstrip() on string |
| 35 | swapcase() Inverts case for all letters in string. |
| 36 | title() Returns "titlecased" version of string, that is, all words begin with uppercase and the rest are lowercase. |
| 37 | translate(table, deletechars="") Translates string according to translation table str(256 chars), removing those in the del string. |
| 38 | upper() Converts lowercase letters in string to uppercase. |
| 39 | zfill (width) Returns original string leftpadded with zeros to a total of width characters; intended for numbers, zfill() retains any sign given (less one zero). |
| 40 | isdecimal() Returns true if a unicode string contains only decimal characters and false otherwise. |
