Lecture 2.1 - Data Types. Data Manipulation (1)

1.

Advanced Programming I
Lecture 2.1 – Data Types and
operations over them
Shynggys Kairatuly Alshynov
MSc in IT
[email protected]

2.

OBJECTIVES
• Identifiers and keywords
• Variables, functions, classes, modules
• Deleting variables
• Naming conventions
• Keywords list
• Data Types
• Numbers and their features https://docs.python.org/3/library/stdtypes.html#numeric-types-intfloat-complex
Integers
Floats
Complex numbers
Decimals
Binaries
Hexs/Octs
• Strings and their features https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str
• Code Examples

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LEARNING OUTCOMES
• At the end of this lecture you will be able to:
• Use different types of variables and their features
• Access and/or change elements of variables
• Give suitable names to variables

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Identifiers
• Identifiers - a name used to identify a variable, function, class,
module or other object. An identifier starts with a letter A to Z or a
to z or an underscore (_) followed by zero or more letters,
underscores and digits (0 to 9)
• Python does not allow punctuation characters such as @, $, and %
within identifiers. Python is a case sensitive programming language.
• Variable is nothing but a reserved space in a memory to store some
values.
• Deleting variables:
• del var_name

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Identifiers naming conventions
• These are naming conventions for Python identifiers:
• Class names start with an uppercase letter. All other identifiers start with a
lowercase letter.
• Starting an identifier with a single leading underscore (_) indicates that the
identifier is private.
• Starting an identifier with two leading underscores (__) indicates a strongly
private identifier.
• If the identifier also ends with two trailing underscores (__name__), the
identifier is a language-defined special name.

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List of keywords
• These are reserved words and you cannot use them as constant or
variable or any other identifier names.

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DATA TYPES – Numbers I
• Numbers are data types that store numeric values. They are
immutable. This means, changing the value of a number data type
results in a newly allocated object.
• int (signed integers) - Integers in Python 3 are of unlimited size.
• float (floating point real values) − represented as decimal point dividing the
integer and the fractional parts. Floats may also be in scientific notation,
with E or e indicating the power of 10 (2.5e2 = 2.5 x 102 = 250).
• complex (complex numbers) − are of the form a + bJ, where a and b are
floats and J (or j) represents the square root of -1 (which is an imaginary
number). The real part of the numbser is a, and the imaginary part is b.
Complex numbers are not used much in Python programming.

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DATA TYPES – Numbers II
• It is also possible to represent integers as binary, hexadecimal or octal
values:
• Hex:
• number = 0xA
• number will be equal to what?
• Oct:
• number = 0o22
• number is equal to ‘I hope you know it guys’
• Binary:
• number = 0b1010
• number is equal to ‘I hope you know it too’

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DATA TYPES – Numbers III
• Number type conversion:
• int(value) – converting to int
• float(value) – converting to float
• complex(value) – converting to complex number with real part equal to
value and imaginary part 0.
• complex(real, imaginary) – converting to complex number with real and
imaginary parts.

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DATA TYPES – Numbers IV
• Math functions for numbers (some examples):
• abs(x) – returns absolute value of a number;
• max([1,2,3,4,9,7,0]) – returns maximum value from inerrable object
• min([1,2,3,4,9,7,0]) – returns minimum value from inerrable object
• pow(x,y) – returns a value of x^y, can be written as x**y
• sqrt(x) – returns square root of x.

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DATA TYPES- STRINGS I
• Strings are amongst the most popular types in Python. We can
create them simply by enclosing characters in quotes. Python treats
single quotes the same as double quotes. No chars.
• String characteristics:
• Immutable
• Indexable
• Sliceable
• Iterable

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DATA TYPES- STRINGS II
• Indexing is accessing a character from a string.
• “Testing value”[4] will return ‘i'
• “This is A”[-1] will return ‘A’
• Slicing is getting a range of indexes:
• “this is some slice testing”[1:4]will return ‘his’
• You can iterate through a string char by char

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DATA TYPES- STRINGS III
• String methods:
• IDLE, YOUR TIME HAS COME
• Use dir(str) to see all the string methods in python interpreter
• Real time demo

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TRICKS – STRINGS
• Autoconcatenation
• print("py" "thon" " is " " fun")
• Multiplication:
• “a”*5 will return “aaaaa”
• Special character avoidance
• print(“D:\Something\name”)
• print(r“D:\Something\name”)
• print(“Is there another way to use ‘quotation marks?’)
• print("Yes, there are. \“You could use it\" before")

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TRICKS – NUMBERS
• Negative Floor (integer) division:
• -22//10 = -3
• Number is rounded down toward the more negative value, because of floor division.
• Negative Floating-Point division (modulo operation)
• -22%10 = 8
• Mathematical reasons
• -22 = 10*i + r, if 0<=r<10, i = -3
• Divisor*i + reminder = Number; condition 0<= reminder < Divisor
• More at
https://docs.python.org/3.6/faq/programming.html#numbers-andstrings

16.

PEP8 – Style Guide For Python
• https://www.python.org/dev/peps/pep-0008/
• Examples:

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SUMMARY
• You obtained(not for sure):
• General knowledge about variables
• Understandings about types like strings, numbers and in python
• Skill to use features of the data types and variables
Congratulations!

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Thank you for your attention!
Python is magical!