My Experiences : March 2022

Thursday, March 31, 2022

Skip some values in array and continue from the value given

Skipp_Test.py

data = ['tab1', 'tab2', 'tab3', 'tab4', 'tab5', 'tab6', 'tab7']

skip_table = True
for d in data:
    if skip_table and d != 'tab3':
        continue
    skip_table = False
    print(d)

Python argparse command line flags without arguments

import argparse

parser = argparse.ArgumentParser(description="Flip a switch by setting a flag")
parser.add_argument('-skip', action='store_true')

where action='store_true' implies default=False.
Conversely, you could haveaction='store_false', which implies default=True.


parser.add_argument('-foo', action='store_const', const=42)
args = parser.parse_args()
print(args.skip)
print(args.foo)

Execution :

python myparser.py
>> False
>> None
python myparser.py -skip
>> True
>> None
python myparser.py -skip -foo
>> True
>>42
python myparser.py -foo
>> False

Logging_Example_Explanation --- import logging

import logging

# This sets the root logger to write to stdout (your console).
# Your script/app needs to call this somewhere at least once.
#logging.basicConfig()

# By default the root logger is set to WARNING and all loggers you define
# inherit that value. Here we set the root logger to NOTSET. This logging
# level is automatically inherited by all existing and new sub-loggers
# that do not set a less verbose level.
logging.root.setLevel(logging.NOTSET)

# The following line sets the root logger level as well.
# It's equivalent to both previous statements combined:
#logging.basicConfig(level=logging.NOTSET)


logger = logging.getLogger("my-app")
f_handler = logging.FileHandler('main-file.log')
f_handler.setLevel(logging.INFO)
f_format = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
f_handler.setFormatter(f_format)
logger.addHandler(f_handler)


# Convenient methods in order of verbosity from highest to lowest
logger.debug("this will get printed")
logger.info("this will get printed")
logger.warning("this will get printed")
logger.error("this will get printed")
logger.critical("this will get printed")
name = 'John'
logger.info('%s raised an error', name)
logger.info('%s raised an information',name)

a = 5
b = 0

try:
  c = a / b
except Exception as e:
  logger.error("Exception occurred", exc_info=True)

a = 5
b = 0
try:
  c = a / b
except Exception as e:
  logger.exception("Exception occurred")

# In large applications where you would like more control over the logging,
# create sub-loggers from your main application logger.
component_a_logger = logger.getChild("component-a")
f_component_a_handler = logging.FileHandler('compoment_a-file.log')
f_component_a_handler.setLevel(logging.ERROR)
f_component_a_handler.setFormatter(f_format)
component_a_logger.addHandler(f_component_a_handler)
component_a_logger.info("INFO: this will get printed with the prefix `my-app.component-a`")
component_a_logger.error("ERROR: this will get printed with the prefix `my-app.component-a`")

# If you wish to control the logging levels, you can set the level anywhere
# in the hierarchy:
#
# - root
#   - my-app
#     - component-a
#


# In large applications where you would like more control over the logging,
# create sub-loggers from your main application logger.
component_b_logger = logger.getChild("component-b")
f_component_b_handler = logging.FileHandler('compoment_b-file.log')
f_component_b_handler.setLevel(logging.ERROR)
f_component_b_handler.setFormatter(f_format)
component_b_logger.addHandler(f_component_b_handler)
component_b_logger.info(" INFO: this will get printed with the prefix `my-app.component-b`")
component_b_logger.error("ERROR: this will get printed with the prefix `my-app.component-b`")

# If you wish to control the logging levels, you can set the level anywhere
# in the hierarchy:
#
# - root
#   - my-app
#     - component-b
#


'''
# Example for development:
logger.setLevel(logging.DEBUG)

# If that prints too much, enable debug printing only for your component:
component_logger.setLevel(logging.DEBUG)

# For production you rather want:
logger.setLevel(logging.WARNING)
'''

Python File Handling: How to Create Text File, Read, Write, Open

How to Open a Text File in Python

To open a file, you need to use the built-in open function. The Python file open function returns a file object that contains methods and attributes to perform various operations for opening files in Python.

Syntax of Python open file function

file_object  = open("filename", "mode")

Here,

filename: gives name of the file that the file object has opened.
mode: attribute of a file object tells you which mode a file was opened in.

More details of these modes are explained below

ow to Create a Text File in Python

With Write to file Python, you can create a .text files (guru99.txt) by using the code, we have demonstrated here:

Step 1) Open the .txt file

f= open("guru99.txt","w+")

We declared the variable “f” to open a file named guru99.txt. Open takes 2 arguments, the file that we want to open and a string that represents the kinds of permission or operation we want to do on the file
Here, we used “w” letter in our argument, which indicates Python write to file and it will create file in Python if it does not exist in library
Plus sign indicates both read and write for Python create file operation.

Step 2) Enter data into the file

for i in range(10):
     f.write("This is line %d\r\n" % (i+1))

We have a for loop that runs over a range of 10 numbers.
Using the write function to enter data into the file.
The output we want to iterate in the file is “this is line number”, which we declare with Python write file function and then percent d (displays integer)
So basically we are putting in the line number that we are writing, then putting it in a carriage return and a new line character

Step 3) Close the file instance

f.close()

This will close the instance of the file guru99.txt stored

Here is the result after code execution for create text file in Python example:

When you click on your text file in our case “guru99.txt” it will look something like this

How to Append Text File in Python

You can also append/add a new text to the already existing file or a new file.

Step 1)

f=open("guru99.txt", "a+")

Once again if you could see a plus sign in the code, it indicates that it will create a new file if it does not exist. But in our case we already have the file, so we are not required to create a new file for Python append to file operation.

Step 2)

for i in range(2):
     f.write("Appended line %d\r\n" % (i+1))

This will write data into the file in append mode.

You can see the output in “guru99.txt” file. The output of the code is that earlier file is appended with new data by Python append to file operation.

Example of How to Append Text File in Python

How to Read Files in Python

You can read a file in Python by calling .txt file in a “read mode”(r).

Step 1) Open the file in Read mode

f=open("guru99.txt", "r")

Step 2) We use the mode function in the code to check that the file is in open mode. If yes, we proceed ahead

if f.mode == 'r':

Step 3) Use f.read to read file data and store it in variable content for reading files in Python

contents =f.read()

Step 4) Print contents for Python read text file

Here is the output of the read file Python example:

How to Read a File line by line in Python

You can also read your .txt file line by line if your data is too big to read. readlines() code will segregate your data in easy to read mode.

When you run the code (f1=f.readlines()) to read file line by line in Python, it will separate each line and present the file in a readable format. In our case the line is short and readable, the output will look similar to the read mode. But if there is a complex data file which is not readable, this piece of code could be useful.

File Modes in Python

Following are the various File Modes in Python:

Mode	Description
‘r’	This is the default mode. It Opens file for reading.
‘w’	This Mode Opens file for writing. If file does not exist, it creates a new file. If file exists it truncates the file.
‘x’	Creates a new file. If file already exists, the operation fails.
‘a’	Open file in append mode. If file does not exist, it creates a new file.
‘t’	This is the default mode. It opens in text mode.
‘b’	This opens in binary mode.
‘+’	This will open a file for reading and writing (updating)

Here is the complete code for Python print() to File Example

Python 2 Example

def main():
     f= open("guru99.txt","w+")
     #f=open("guru99.txt","a+")
     for i in range(10):
         f.write("This is line %d\r\n" % (i+1))
     f.close()   
     #Open the file back and read the contents
     #f=open("guru99.txt", "r")
     #   if f.mode == 'r': 
     #     contents =f.read()
     #     print contents
     #or, readlines reads the individual line into a list
     #fl =f.readlines()
     #for x in fl:
     #print x
if __name__== "__main__":
  main()

Python 3 Example

Below is another Python print() to File Example:

def main():
    f= open("guru99.txt","w+")
    #f=open("guru99.txt","a+")
    for i in range(10):
         f.write("This is line %d\r\n" % (i+1))
    f.close()
    #Open the file back and read the contents
    #f=open("guru99.txt", "r")
    #if f.mode == 'r':
    #   contents =f.read()
    #    print (contents)
    #or, readlines reads the individual line into a list
    #fl =f.readlines()
    #for x in fl:
    #print(x)
if __name__== "__main__":
  main()

Summary

Python allows you to read, write and delete files
Use the function open(“filename”,”w+”) for Python create text file. The + tells the python interpreter for Python open text file with read and write permissions.
To append data to an existing file or Python print to file operation, use the command open(“Filename”, “a“)
Use the Python read from file function to read the ENTIRE contents of a file
Use the readlines function to read the content of the file one by one.

Reference :

https://www.guru99.com/reading-and-writing-files-in-python.html

My Experiences