Python String index () and its applications

File handling | Python functions | String Variables

Michael Zippo 18.07.2021

Search for a string (substring) in the string — it is an application that is used many times in daily life. Python offers this with the index () function, which returns the position of the first occurrence of a substring in a string

  Syntax:  ch.index (ch1, begp, endp)  Parameters:   ch1:  The string to be searched for.  begp (default: 0):  This function specifies the position from where search has to be started.  endp (default: string_len):  This function specifies the position from where search has to end.  Return Value:  Returns the first position of the substring found.  Exception:  Raises ValueError if argument string is not found.

       # Python code to demonstrate how it works  
  # metric ()  
   
  # target string initialization  
   ch   =   "pythonengineering"  
   
  # argument string initialization  
   ch1   =   "geeks"  
   
  # using index () to find the position of the geeks  
  # starting at the second index  
  # prints 8  
   pos   =   ch.index (ch1,   2  )  
   
   print   (  "The first position of geeks after 2nd index:"  , end   =   "") 
   print   (pos)

Output:

 The first position of geeks after 2nd index : 8

Exceptions

ValueError: This error occurs when the argument string is not found in the target string.

# Python code to demonstrate the exception
# metric ()

# target string initialization

ch = "pythonengineering"

# initialize the argument string

ch1 = "gfg"

# using index (), to find the position & quot; gfg & quot;
# throws an error

pos = ch.index (ch1)

print ( "The first position of gfg is: " , end = " ")

print (pos)

Runtime Error:

 Traceback (most recent call last): File "/home/aa5904420c1c3aa072ede56ead7e26ab.py", line 12, in pos = ch.index (ch1) ValueError: substring not found

Practical Application: This function is used to extract the suffix or prefix length after or before the target word . The example below shows the total command length in bits derived from AC voltage given the information in the line.

# Python code to demonstrate usage
# metric ()

# initializing target strings

voltages = [ "001101 AC" , "0011100 DC" , "0011100 AC" , "001 DC" ]

# initialize the argument string

type = "AC"

   
  # initializing the length calculator  
   sum_bits   =   0  
   
   for   i   in   voltages:  
   
    ch   =   i

if (ch [ len (ch) - 2 ]! = ’D’ ):

# extracts the length of the bits in a string

bit_len = ch.index ( type ) - 1

# adds to total

sum_bits = sum_bits + bit_len

print ( "The total bit length of AC is:" , end = "")

print (sum_bits)

Exit :

 The total bit length of AC is: 13

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Python String index () and its applications

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