Category: C#

There are some differences in control flow in C# and Python though the concept in both languages is pretty much the same. Let’s take a look at them.

1. Entry point
   The entry point to Python program can be expressed like the following. class is NOT necessary in Python, so if you are working on a simple script, I would just start to write logic in the file without a class. That said, I still like to encapsulate everything classes.

   class Main:
       def __init__(self):
           pass
   
       def say_hello(self):
           print('hello Python!')
   
   
   if __name__ == '__main__':
       entry_class = Main()
       entry_class.say_hello()
   

2. if elif else
   Let’s think about the function that returns month name in a string.

       def get_month_name(num):
           if num == 1:
               return "January"
           elif num == 2:
               return "February"
           elif num == 3:
               return "March"
           elif num == 4:
               return "April"
           elif num == 5:
               return "May"
           elif num == 6:
               return "June"
           elif num == 7:
               return "July"
           elif num == 8:
               return "August"
           elif num == 9:
               return "September"
           elif num == 10:
               return "October"
           elif num == 11:
               return "November"
           elif num == 12:
               return "December"
           else:
               return "Invalid number" # Could throw an error

   I know the sample is ugly, but you get the idea. switch statement is NOT available in Python unfortunately but there is a workaround. I will write about in a separate blog post.

3. while

   i = 0
   while i < 100:
       print(i)
       i += 1

   Not so elegant but while is still a necessary control statement.

4. for

   nums = [1, 2, 3, 4, 5, 6, 7, 8, 9]
   for n in nums:
       print(n)

   for in Python acts like foreach in C#. If you want to express something like for (int i = 0; i < nums.length; i++) {}, you can do something like the following.

   for n in range(1, 10):
       print(n)

   The sample shows that range function can be used to mimic “for (int i = 0; i < nums.length; i++) {}” in C#.

try, catch/except, finally is a necessary control flow in any modern programming language. Here is one in C#.

var obj = new MyObj();

try
{
    obj.func1("bad data"); // This line can cause an error.
    // Do some other work here if error didn't happen.
}
catch(SomeException exp)
{
   ExceptionHandler(exp);
}
finally
{
    obj.CleanUp();
}

Here is the sample in Python.

obj = MyObj()

try:
    obj.func1("bad data") # This line can cause an error.
except SomeError as exp:
    exception_handler(exp)
else:
    # Do some other work here if error didn't happen.
finally:
    obj.clean_up()

Notice that Python can have else clause but it’s not necessary to use it. I would use it if I want a very clear separation between “trying code” and the process after it.

There may be situations where you need to raise errors. You can simply use raise keyword like the example below.

raise ValueError("Entered value is not valid.")

There are quite a bit of builtin error types. They can be found in this document.

Lastly, if you need to create your own exception type, you can create a class that inherits from Exception class.

class MyError(Exception):
    pass

I think I wrote C# code the most in my career. C# is almost like a mother tongue to me just like Japanese language is though I’ve been speaking “foreign languages” like Groovy and Python quite a bit. When I have to think deep about something, I always go back to my mother tongue. I think I’m going to try it out with C#. In this series, I’m going to write some sample code in C# and then translate it into Python.

I won’t start like what variables are, strings are, integers are… those very basic concepts like in any other “tutorial” sites. I will go straight into what may be useful.

I’m going to talk about functions this time. Functions can be void or ones that return something. Let’s see them in C#.

using System.IO;

public class Functions
    {
        public void WriteString(string path, string text)
        {
            File.WriteAllText(path, text);
        }

        public int Add(int a, int b)
        {
            return a + b;
        }
    }

Now let’s see them in Python.

class Functions:
    def WriteString(self, path, text):
        with open(path, 'w') as f:
            f.write(text)

    def Add(self, a, b):
        return a + b

This is not really “Pythonic”. Let’s change the Python code into more Pythonic way.

class functions:
    def write_string(self, path, text):
        with open(path, 'w') as f:
            f.write(text)

    def add(self, a, b):
        return a + b

Python coding standard is, in short, lower case everything connecting words with underscore. The details can be found here.

It’s very easy to see what the differences are but I will try to explain in words.

return keyword returns a value to the caller of the function.

To create a class, Python uses the same “class” keyword. Whenever you use a keyword (such as if, while, for and etc…), it has to end with : (semi colon). When you define a function, it has to start with def. There is no distinction between function that returns value or not.

“with” keyword in Python is equivalent to using in C#. It makes sure that any resource (such as file, database or network connection) opened this way will be closed when the code gets out of the context. (context manager)