Pages

Saturday, October 29, 2022

Mastering String Manipulation in Python: An Introduction to Strings and String Slicing

Strings


Strings in python are defined by enclosing with either single quotation marks (") or double quotation marks (")

1

2

str_hello = "Hello..."

str_hello = 'Hello...'

It does not make a difference in the way string is stored and/or used in the program based on the way it is declared (i.e., by using single quotation marks or double quotation marks). 

Multi-line strings

Above declaration is applicable when the string is of a single line. If we have a string that has multiple lines, multi-line string can be defined by enclosing with either three single quotation marks (''') and double quotation marks (""").

1

2

3

4

5

6

7

multi_string = """Hello World,

This is a multi-line string.

enclosed in double quotation marks"""

 

multi_string = '''Hello World,

This is a multi-line string.

enclosed in single quotation marks'''

Accessing part of the string by using index

String is similar to an array of characters (there is no character data type in Python) and Index starts from 0.

1

2

3

str_hello = "Hello..."

print(str_hello[0]) # H

print(str_hello[1]) # e


Similarly data can be accessed using negative index (i.e., -1 for the last position) 

1

2

3

str_hello = "Hello..."

print(str_hello[-1]) # .

print(str_hello[-4]) # o


Below are the index positions of a string from above example. 

H e l l o . . .

0 1 2 3 4 5 6 7

-8-7-6-5-4-3-2-1

Looping through the string

We mentioned that the string is like an array of characters and we can access the specific character using it's index. 

So, how to loop through all the characters of a string? There are two ways to achieve this.
  • Retrieve string length and loop through the range and access character by using index.
  • Loop through the string directly. 
So, How to calculate the length of the string? 'len()' function returns length of a string. 

1

2

3

string = "Hello World"

for i in range(len(string)):

   print(string[i])


In this example, for loop repeats for every character in the string and character can be accessed by the variable specified (char in this example) through out the loop.

1

2

3

string = "Hello World"

for char in string:

   print(char)


What is string slicing? 

By using the index we can only access one character at a time. We can use slicing to retrieve portion of the string. 

For slicing, we need to provide the starting index (included) and ending index (not included in result). 

1

2

3

4

5

6

7

8

'''

Hello World

012345678910

'''

 

string = "Hello World"

print(string[0:5]) # Hello

print(string[2:5]) # llo


In the above example (Line - 7), we are passing index '0' (as the starting position) and index '5' (as the ending position, not included) which returns the part of the string 'Hello'. Value in the index 5 (' ') is not included in the result. 

In Line - 8, we are passing index '2' and '5', which would return the portion of the string from 2 to 4 (both included).

In the cases like Line - 7 where we are retrieving the porting of the string from beginning till the specified index, we won't really need to include index '0'. 

1

2

string = "Hello World"

print(string[:5]) # Hello


Leaving the start index would consider the string from the beginning. 

Similarly if we leave off end index, it would return the string from start index till end. 

1

2

string = "Hello World"

print(string[6:]) # World


So, what happens if we don't mention both start and end index? It returns the full string. 

1

2

string = "Hello World"

print(string[:]) # Hello World


Check if a character/string present in the string

We have seen how to access a character or a portion of string from a string. Now, Can we check if a character or a string is part of the string or not? Yes, we can do this by using 'in' and 'not in'.

1

2

3

string = "Hello World"

print('H' in string) # True

print('H' not in string) # False


In the above example,
  • Line - 2: We are checking if 'H' is in the string, which returns True if present and False if not present. 
  • Line - 3: We are checking if 'H' is not in the string, which returns False if present and True if not present. 
Similarly, we can use a string to check if it is part of another string. 

1

2

3

string = "Hello World"

print('Hello' in string) # True

print('Hello' not in string) # False


It is highly unlikely we use 'in' and 'not in' operator the way we have described (this is only for better understanding). 

Most likely we would be using this in a condition. 

1

2

3

4

5

string = "Hello World"

if 'Hello' in string:

   print('Hello is present in the string')

else:

   print('Hello is not present in the string')


1

2

3

4

5

string = "Hello World"

if 'Hello' not in string:

   print('Hello is not present in the string')

else:

   print('Hello is present in the string')



We have seen how to define a string & multi-line string, accessing a portion of the string (string slicing) and checking if a character or string is part of the string or not. Hope this has been a bit of help in understanding the use of strings in Python.


If you have any Suggestions or Feedback, Please leave a comment below or use Contact Form.

Thursday, October 27, 2022

View Binding Directory Entries from SQL - IBM i

View Binding Directory Entries


Binding directory is an object that holds the list of modules and/or service programs that may be required for the compilation of ILE programs. 

In other words, Binding directory contains modules and/or service programs whose procedures might be used across different ILE programs and are required for compiling the ILE programs. 

Can these programs be compiled without the use of binding directory? The answer is Yes. If a program is using procedures from one service program (say SRVPGM1), corresponding service program to be added against the parameter BNDSRVPGM when creating the program using CRTPGM. 

So, Why is binding directory needed? In the above scenario, we are only talking about one program using procedure from one service program so it is easy to mention service program name while creating a program. Say if we have many procedures across different service programs (most common), It becomes hard to remember and adding all the service program names while compiling. 

Binding directory provides the option to add all the modules and service programs whose procedures could be used in various programs. And, binding directory name can either be added in the H spec of the RPGLE source or against BNDDIR parameter in the compilation command (CRTPGM, CRTBNDRPG...). 

How do we view the entries in binding directory? Traditionally, DSPBNDDIR (Display Binding Directory) command is used to display the entries in binding directory. 

DSPBNDDIR BNDDIR(<library>/<binding-directory>) 

Same information can now be viewed from the SQL by running a SELECT query on the view BINDING_DIRECTORY_INFO (system name - QSYS2/BNDDIR_INF). 

This view contains the same information as it is displayed using DSPBNDDIR. 
  • BINDING_DIRECTORY_LIBRARY - The library which contains the binding directory.
  • BINDING_DIRECTORY - The binding directory name.
  • ENTRY_LIBRARY - The library containing entry (i.e., service program or module). Can contain the special value *LIBL.
  • ENTRY - The name of the binding directory entry.
  • ENTRY_TYPE - The object type of the binding directory entry. Valid values are *MODULE and *SRVPGM.
  • ENTRY_ACTIVATION - The activation control of the bound service program. Valid values are *DEFER (Activation of the bound service program may be deferred until a function it exports is called) and *IMMED (Activation of the bound service program takes place immediately when the program or service program it is bound to is activated). Contains the null value if ENTRY_TYPE is *MODULE.
  • ENTRY_CREATE_TIMESTAMP - The timestamp when the object was created. Contains the null value if the entry timestamp is not available.
There are two major advantages of using the SQL view (BINDING_DIRECTORY_INFO) over the command DSPBNDDIR. 
  • There is no provision for filter to check for a specific entry in the binding directory in DSPBNDDIR. So one has to page down and find out to see if the specific entry is  present in binding directory. 
  • One has to run command DSPBNDDIR on multiple binding directory to find out all the binding directories in which a specific entry is added. 
Both of these can be easily achieved with the use of SQL view. 

Check for the entries starting with TEST in a specific binding directory. 

SELECT * FROM QSYS2.BINDING_DIRECTORY_INFO
WHERE BINDING_DIRECTORY_LIBRARY = 'TESTLIB'
AND BINDING_DIRECTORY = 'TESTBNDDIR' 
AND ENTRY LIKE 'TEST%';

Check for the binding directory which has entry TESTSRVPGM and entry library TESTLIB. 

SELECT * FROM QSYS2.BINDING_DIRECTORY_INFO
WHERE   ENTRY_LIBRARY = 'TESTLIB'
AND   ENTRY LIKE 'TESTSRVPGM'
AND   ENTRY_TYPE = '*SRVPGM';

Similarly, we can run the query based on the entry activation, entry create timestamp or any other fields as required.


If you have any Suggestions or Feedback, Please leave a comment below or use Contact Form.

Removing elements from a list in Python with list method pop()

Removing elements from a list It's often essential to remove the data from any data set (let's take 'list' in this case).  T...