Python Course: Basics

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# Python Course: Basics
        Shahid Beheshti University
        Instructor: S. M. Masoud Sadrnezhaad

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# What's Python

- Python is a widely used **general-purpose**, **high-level** programming language.

- Its design philosophy emphasizes **code readability**.

- Its syntax allows programmers to express concepts in **fewer lines of code** than would be possible in languages such
    as C++ or Java.

- Python supports **multiple programming paradigms**.

- It features a **dynamic type system** and **automatic memory management** and has a **large and comprehensive
    standard library**.

- Python interpreters are available for **many operating systems**.

---

# Python 2.x vs 3.x

- Python 2.0 was released in 2000, with many new features added.

- Python 3.0, adjusting several aspects of the core language, was released in 2008.

- Python 3.0 is **backwards-incompatible**.

- Python 2.x is legacy, Python 3.x is the present and future of the language.

- We use Python 3.x in this course. (3.7.0 at the moment)

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# Python Installation

- Go to http://www.python.org and follow the instructions for installing Python 3.

- Python Shell

- PyCharm IDE

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# Hello, world!

```python
print("Hello, world!")
```

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# Let's see something serious!

- No semi-colons. Indentation matters.

```python
SUFFIXES = {1000: ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'],
            1024: ['KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB', 'ZiB', 'YiB']}

def approximate_size(size, a_kilobyte_is_1024_bytes=True):
    '''Convert a file size to human-readable form.

Keyword arguments:
    size -- file size in bytes
    a_kilobyte_is_1024_bytes -- if True (default), use multiples of 1024
                                if False, use multiples of 1000

Returns: string

'''
    if size < 0:
        raise ValueError('number must be non-negative')

multiple = 1024 if a_kilobyte_is_1024_bytes else 1000
    for suffix in SUFFIXES[multiple]:
        size /= multiple
        if size < multiple:
            return '{0:.1f} {1}'.format(size, suffix)

raise ValueError('number too large')

if __name__ == '__main__':
    print(approximate_size(1000000000000, False))
    print(approximate_size(1000000000000))
```

---

# Variables

- Python is a dynamically typed language.

- Python has has typed objects but untyped variable
names.

```python
>>> my_var = 2
>>> type(my_var)
<class 'int'>
>>> my_var = "hi there!"
>>> type(my_var)
<class 'str'>
```

---

# Basic Data Types

Booleans: True, False

- bool

Strings: "a string", 'another string'

- str

Numbers: 42, 159.523, 4j

- int, float, complex

None

---

# Operators

- Basic operators

- Arithmetic (`+`, `-`, `*`, `**`, `/`, `%`, `//`)
  - Assignment (`=`, `+=`, `-=`, `*=`, `**=`, `/=`, `%=`, `//=`)
  - Comparison (`<`, `>`, `<=`, `>=`, `==`, `!=`)
  - Logical (`and`, `or`, `not`)

- Bitwise operators

- `x << y`: Returns x with the bits shifted to the left by y places (and new bits on the right-hand-side are zeros). This is the same as multiplying x by `2**y`.
  - `x >> y`: Returns x with the bits shifted to the right by y places. This is the same as //'ing x by `2**y`.
  - `x & y`: Does a "bitwise and".
  - `x | y`: Does a "bitwise or".
  - `~ x`: Returns the complement of x two’s complement.
  - `x ^ y`: Does a "bitwise exclusive or".

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# Type Conversion

- Python is **strongly typed**, forbidding operations that are not well-defined, rather than silently attempting to make
sense of them (compare with JavaScript).

```python
>>> 'Masoud' + ' ' + 'Sadrnezhaad'
'Masoud Sadrnezhaad'
>>> 'ha' * 10
'hahahahahahahahahaha'
>>> 'ten' + 5
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Can't convert 'int' object to str implicitly
>>> 'ten' + str(5)
'ten5'
```

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# Truth Value Testing

- Any object can be tested for truth value, for use in a condition.

- The following values are considered False

- None
  - False
  - 0, 0.0, 0j
  - Any empty sequence, set or dictionary:
    - '', "", {}, [], (), etc.

- The rest is True.

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# References

- Dr. Hamid Zarrabi-Zadeh's Web Course, Fall 2013.

- http://www.diveintopython3.net/

- http://openbookproject.net/thinkcs/python/english3e/

- http://en.wikipedia.org/wiki/Python_(programming_language)

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# Thank you.
    Any questions?