Table of contents
Tutorial Day 3

String

In Python, strings are used to store text or alphanumeric data. Strings are represented by enclosing the data in single quotes (') or double quotes (").

Strings are a sequence type, meaning their characters are ordered and can be accessed using indices.

Strings belong to the built-in str class in Python.

You cannot use single or double quotes for multi-line text. It will cause a SyntaxError

# Using double quotes string1 = "Hello, Python!" # Using single quotes string2 = 'Hello, World!' print(string1, type(string1)) print(string2, type(string2))

Type of Strings.

Python allows you to store string data in two main ways. Those are

  • Single-line string
  • Multi-line string 

Single -line string.

  • These are strings that are written on one line. We can use either single quotes or double quotes.
  • We can`t use single or double quotes to organize multi-line string data.
# single quotes name = 'Hello Python' print(name) # double quotes var = 'Hello Cedlearn' print(var)
# Error str = " hello Python" The Multi Line string data is one , which is enclosed within tripple single Quotes or tripple double quotes.

Multi-line string

  • Multi-line strings can be created using either triple  single quotes (''') or triple double quotes ("""). These strings can span multiple lines  
  • String literals that span multiple lines for improved readability.
addr1="""Guido van Rossum HNO:3-4, Red seaside Python Software Foundation Centrum Wiscunde Informatica Nether Lands """ print(addr1,type(addr1))

Operation on String data

On string, we can perform the two types of operations.

  1. Indexing
  2. Slicing

Indexing

  • The process of obtaining an element by giving a string object and passing a valid index value.
  • The index can either be Positive or Negative.
  • The positive index starts with 0 and the negative index starts with -1. 
  • If we enter a valid index then get values at that index. If you enter an invalid index  then get IndexError  
# Positive index my_str = "Python" print(my_str[0]) print(my_str[1]) print(my_str[2]) print(my_str[3])
# IndexError my_str = "Python" print(my_str[10])
Positive index and Negative index
Positive index and Negative index

Slicing

  • The process of obtaining the range of characters or sub-strings of the main string is called slicing.
  • The syntax string[Begin:End] extracts characters from the "Begin" index (inclusive) to the "End" index - 1 (exclusive).  
  •  If Begin Index >= End Index, the result is an empty output ('') .
# slicing using +ve index my_str = "Python" print(my_str[2:4]) print(my_str[1:6]) print(my_str[4:2]) # empty
# Slicing with -ve index my_str = "Python" print(my_str[-4:-2]) print(my_str[-6:-1]) print(my_str[-10:-1]) # Python print(my_str[-1:-5])# empty
  • If the Begin Index and End Index are not specified, Python assumes the End Index as len(strobj) - 1.
  • This syntax retrieves characters starting from the Begin Index to the last character of the string object (len(strobj) - 1).
# s="PYTHON" print(s[2:])-----------THON print(s[1:])----------YTHON print(s[4:])-------ON print(s[-2:])---------ON print(s[-6:])-------PYTHON print(s[0:])--------PYTHON print(s[-2:])-------ON print(s[-5:])-------YTHON
  • If the Begin Index is not specified and the End Index is specified, Python assumes the Begin Index as the initial index (0).
  • This syntax retrieves characters from the initial index (0) to End Index - 1 of the string object.
s="PYTHON" print(s[ : 5] )------------PYTHO print(s[ : 5])------------PYTHO print(s[ : 2])-----------PY print(s[ : 3])----------PYT print(s[ :-3])---------PYT print(s[ :-4])--------PY print(s[ :-6])-----empty
  • If neither the Begin Index nor the End Index is specified, Python assumes the Begin Index as the initial index (0) and the End Index as len(strobj) - 1.
  • This syntax retrieves the complete data of the string object.
s="PYTHON" >>> print(s[ : ])--------PYTHON >>> print(s)------PYTHON
  • The syntax strobj[BEGIN:END:STEP] allows slicing with an optional step value, where the default value of STEP is 1, processing the string in a forward direction.
  • If STEP is positive, it slices characters from BEGIN to END - 1 in a forward direction (left to right).
  • If STEP is negative, it slices characters from BEGIN to END + 1 in a backward direction (right to left).
  • When slicing forward, an END value of 0 results in no output.
  • When slicing backward, an END value of -1 results in no output.
# Slicing with step value s="PYTHON" print(s[0:6:2])----------PTO print(s[0:6:3])---------PH print(s[2:6:3])---------TN print(s[-6:-3:2] )-------PT print(s[ :4:2])--------PT print(s[3: :2])----------HN print(s[ : : 2])--------PTO print(s[ : : 1])--------PYTHON
s="PYTHON" print(s[2:6:-1])------- No output print(s[6:2:-1])--------NOH print(s[5:0:-2])-------NHY print(s[::-2])--------NHY print(s[::-1])----------NOHTYP
s="NAYAN" print(s[::1])------NAYAN print(s[::-1])----------NAYAN print(s[:0:1])---No Output print(s[:-1:-1])-----No Output
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