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June 16, 2022 Post a Comment

Introduction to Python Parser

In this article, parsing is defined as the processing of a piece of python program and converting these codes into machine language. In general, we can say parse is a command for dividing the given program code into a small piece of code for analyzing the correct syntax. In Python, there is a built-in module called parse which provides an interface between the Python internal parser and compiler, where this module allows the python program to edit the small fragments of code and create the executable program from this edited parse tree of python code. In Python, there is another module known as argparse to parse command-line options.

Working of Python Parse

In this article, Python parser is mainly used for converting data in the required format, this conversion process is known as parsing. As in many different applications data obtained can have different data formats and these formats might not be suitable to the particular application and here comes the use of parser that means parsing is necessary for such situations. Therefore, parsing is generally defined as the conversion of data with one format to some other format is known as parsing. In parser consists of two parts lexer and a parser and in some cases only parsers are used.

Python parsing is done using various ways such as the use of parser module, parsing using regular expressions, parsing using some string methods such as split() and strip(), parsing using pandas such as reading CSV file to text by using read.csv, etc. There is also a concept of argument parsing which means in Python, we have a module named argparse which is used for parsing data with one or more arguments from the terminal or command-line. There are other different modules when working with argument parsings such as getopt, sys, and argparse modules. Now let us below the demonstration for Python parser. In Python, the parser can also be created using few tools such as parser generators and there is a library known as parser combinators that are used for creating parsers.

Examples of Python Parser

Now let us see in the below example of how the parser module is used for parsing the given expressions.

Example #1

Code:

              import parser print("Program to demonstrate parser module in Python") print("\n") exp = "5 + 8" print("The given expression for parsing is as follows:") print(exp) print("\n") print("Parsing of given expression results as: ") st = parser.expr(exp) print(st) print("\n") print("The parsed object is converted to the code object") code = st.compile() print(code) print("\n") print("The evaluated result of the given expression is as follows:") res = eval(code) print(res)

Output:

In the above program, we first need to import the parser module, and then we have declared an expression to calculate and to parse this expression we have to use a parser.expr() function. Then we can evaluate the given expression using eval() function.

In Python, sometimes we get data that consists of date-time format which would be in CSV format or text format. So to parse such formats in proper date-time formats Python provides the parse_dates() function. Suppose we have a CSV file that contains data and the data time details are separated with a comma which makes it difficult for reading therefore for such cases we use parse_dates() but before that, we have to import pandas as this function is provided by pandas.

In Python, we can also parse command-line options and arguments using an argparse module which is very user friendly for the command-line interface. Suppose we have Unix commands to execute through a python command-line interface such as ls which list all the directories in the current drive and it will take many different arguments also therefore to create such a command-line interface we use an argparse module in Python. Therefore, to create a command-line interface in Python we need to do the following; firstly, we have to import an argparse module, then we create an object for holding arguments using ArgumentParser() through the argparse module, later we can add arguments the ArgumentParser() object that will be created and we can run any commands in Python command line. Note as running any commands is not free other than the help command. So here is a small piece of code for how to write the python code to create a command line interface using an argparse module.

              import argparse

Now we have created an object using ArgumentParser() and then we can parse the arguments using parser.parse_args() function.

              parser = argparse.ArgumentParser() parser.parse_args()

To add the arguments we can use add_argument() along with passing the argument to this function such as parser.add_argument(" ls "). So let us see a small example below.

Example #2

Code:

              import argparse parser = argparse.ArgumentParser() parser.add_argument("ls") args = parser.parse_args() print(args.ls)

Output:

So in the above program, we can see the screenshot of the output as we cannot use any other commands so it will give an error but when we have an argparse module then we can run the commands in python shell as follows:

              $ python ex_argparse.py --help usage: ex_argparse.py [-h] echo

Positional Arguments:

              echo

Optional Arguments:

              -h, --helpshow this help message and exit $ python ex_argparse.py Educba Educba

Conclusion

In this article, we conclude that Python provides a parsing concept. In this article, we saw that the parsing process is very simple which in general is the process of parting the large string of one type of format for converting this format to another required format is known as parsing. This is done in many different ways in Python using python string methods such as split() or strip(), using python pandas for converting CSV files to text format. In this, we saw that we can even use a parser module for using it as a command-line interface where we can run the commands easily using the argparse module in Python. In the above, we saw how to use argparse and how can we run the commands in Python terminal.

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