Underscore(_) in Python

In Python in some cases we use Single Underscore(_) and some cases we use Double Underscores (__).

In Python has following cases, where we use underscore.

• If we want to store the value of last expression in interpreter.
• If we want to ignore some values.
• For declaration of variable or function.
• To separate digits of number lateral value.
• It is also used as ?Internationalization (i18n)' or ?Localization (l10n)' functions.

Now some examples on every cases.

Used in interpreter

The Python Interpreter stores the last expression value in the '_'.

 >>> 20 20 >>> _ 20 >>> _ + 3 23 

Ignoring the values

Underscore is also used for ignoring the values.

 x, _, y = (1, 2, 3) 

Here x = 1, y = 3 and ignore the value 2.

Used for declaring variable and function

Python does not support private, so we cannot force something's private ones but we can call it directly from other modules.

 single_trailing_underscore_ 

Using this conversion easily can avoid conflicting of Python keywords and built-ins.

 __double_leading_underscore 

This is mangle, it is used to avoid conflicts of attributes name between names.

If you write a method name "__display" in a class, the name will be mangled in "_ClassName__display" form.

 __double_leading_and_trailing_underscore__ 

In some cases we use this conversion. Just like _init_.

To separate digits of number lateral value

 dec_base = 1_000_000 print(dec_base) # 1000000 

As Internationalization (i18n)/Localization (l10n) functions

This is just a convention not any syntactic functions here underscore just bind the i18n/l10n to underscore variable has been from C convention.