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+---
+aliases: ["under"]
+embed:
+    title: "Meanings of Underscores in Identifier Names"
+---
+
+• `__name__`: Used to implement special behaviour, such as the `+` operator for classes with the `__add__` method. [More info](https://dbader.org/blog/python-dunder-methods)
+• `_name`: Indicates that a variable is "private" and should only be used by the class or module that defines it
+• `name_`: Used to avoid naming conflicts. For example, as `class` is a keyword, you could call a variable `class_` instead
+• `__name`: Causes the name to be "mangled" if defined inside a class. [More info](https://docs.python.org/3/tutorial/classes.html#private-variables)
+
+A single underscore, **`_`**, has multiple uses:
+• To indicate an unused variable, e.g. in a for loop if you don't care which iteration you are on
+```python
+for _ in range(10):
+    print("Hello World")
+```
+•  In the REPL, where the previous result is assigned to the variable `_`
+```python
+>>> 1 + 1  # Evaluated and stored in `_`
+    2
+>>> _ + 3  # Take the previous result and add 3
+    5
+```
+• In integer literals, e.g. `x = 1_500_000` can be written instead of `x = 1500000` to improve readability
+
+See also ["Reserved classes of identifiers"](https://docs.python.org/3/reference/lexical_analysis.html#reserved-classes-of-identifiers) in the Python docs, and [this more detailed guide](https://dbader.org/blog/meaning-of-underscores-in-python).