# Python

(Redirected from Number)
Python is the main programming language for 61A.

## Data types

Every value is an object. The following are the most commonly used Python data types:

### Number

A number can be an integer or a float. An integer can be converted to a float using the `float()` constructor, and a float can be converted to an integer using the `int()` constructor.

Examples:

```>>> 2 # integer
2
>>> 2.0 # float
2.0
>>> int(2.0)
2
>>> float(2)
2.0```

### Boolean

A boolean has only two possible values: `True` or `False`. The type of a boolean is `bool`. Comparison operators return booleans:

```>>> 1 > 2
False
>>> 1 < 2
True
>>> 's' == 's'
True```

In a boolean context, all values evaluate to `True` except the following, which evaluate to `False`:

```None
0
""
[]
()
{}
set()```

### String

Main article: Sequence#String

### Tuple

Main article: Sequence#Tuple

### List

Main article: Sequence#List

### Dictionary

Main article: Dictionary

### Set

Main article: Set

## Operators

Main article: Operator

## Statements and expressions

Computer programs are generally made up of statements and expressions:

• Statements carry out actions. A program executes a statement. Examples include the `def`, `import`, `return`, and assignment (`=`) statements.
• Expressions compute some value. A program evaluates an expression. Expressions can include anything from primitives (`True`, `2`, `3`, `2.0`) to lengthy call expressions.

## Function call

A function call is executed in the following way:

• create a new local frame
• bind arguments to formal parameters in that frame
• execute the body

## Iteration

Main article: Iteration

Iteration is the process of repeatedly executing a block of code.

## Command Line

To start a Python interpreter, one can just type python3 into the command line, or the name of the command that leads to the Python 3 program:

`python3`

To run a Python file, one should include the file path. Any additional arguments provided can be accessed via `sys.argv`.

```python3 path/to/file.py
python3 path/to/file.py arg1 arg2 ...```

To run a Python file and then continue execution with an interactive session, add the `-i` flag.

`python3 -i path/to/file.py`

## Testing

Python has a lot of built-in support for testing. The two testing modules used for this course are `doctest` and `unittest`.

• Doctest - Find docstrings that model interactive sessions and compare the output specified in the docstrings to the actual output from the program.
• Unittest - Organize test code into units and then run the units together, logging the tests that succeeded and the ones that failed.