7/29/2019 Lecture#2: Introductory Python

1/21

High performance computing

for non-programmers

Lecture #2:Python programminglanguage: Overview

Glib Ivashkevych

junior researcher, NSC KIPT

7/29/2019 Lecture#2: Introductory Python

2/21

cross-platform

simple to learn

general-purpose

flexible & extendable

Huge standard library

Tons of third-party packages

Documentation

7/29/2019 Lecture#2: Introductory Python

3/21

web-development

scripting in VFX

science & engineering

system administration

Youtube, Google, Instagram, DropBox

NASA, CERN

Philips, ILM and more

Is used for:

7/29/2019 Lecture#2: Introductory Python

4/21

data processing

glue layer

GUI

code generation & prototyping

Python has a lot of tools for scientific

computing: NumPy, SciPy, SymPy, scikit-learn

In computing:

7/29/2019 Lecture#2: Introductory Python

5/21

Scripting Compiled

language instructions areexecuted one by one

flexible, but slow

allow for very fastdevelopment cycle

perfect forcomplex automation

language instructions arecompiled to assembly

rigid, but fast

development cycle is usuallylonger

perfect forperformance

7/29/2019 Lecture#2: Introductory Python

6/21

How Python code is

executed

file.py file.pyc

sourcecode

bytecode

file.pyc

PythonVirtual

Machine

compilation

execution

7/29/2019 Lecture#2: Introductory Python

7/21

Python type system

Dynamic,

variables are references

no definitions, created automatically

but strong typing

objects have type

+ garbage collector

7/29/2019 Lecture#2: Introductory Python

8/21

x == y x is y

some string

x

y

True True

7/29/2019 Lecture#2: Introductory Python

9/21

x == y x is y

some string

x

y

True False

some string

7/29/2019 Lecture#2: Introductory Python

10/21

Mutable vs Immutable

Mutable objects can be changed

lists, dictionaries, sets, byte arrays

can be changed in-place

Immutable objects can not be changed once

creatednumbers, strings, tuples

new object is created at each

reassignment

7/29/2019 Lecture#2: Introductory Python

11/21

Naming

First symbol_ (underscore) or letter

Symbols_ (underscore), letters, digits

_myfunc

__somemagic

generate_file

generate-file

6func

fancy#name

7/29/2019 Lecture#2: Introductory Python

12/21

Numbers

Integer32 bit -2147483648...2147483647

long - arbitrary

boolean - True, False

Floatdouble precision, no support for single precision

Complextwo double precision numbers

7/29/2019 Lecture#2: Introductory Python

13/21

Sequences

List (mutable)

[1,2,Hello World, True]

Tuple (immutable)

(1,2,Hello World, True)

String (immutable)

HPC, new string, Some multiline string

7/29/2019 Lecture#2: Introductory Python

14/21

Mappings

Dictionary (mutable)

key-value storage

my_dict = {a:2, string:42, (1,2,3): [1,2,3]}

my_dict[a] == 2 #True

my_dict[(1,2,3)] == [1,2,3] #True

Only immutable types can be a key

7/29/2019 Lecture#2: Introductory Python

15/21

Logic

and, or, not

non-zero numbers, non-empty objects: True

zero-numbers, empty-objects, None: Falsecomparison and equality: True or False

and, or: return operand

if elif ... else statement

a ifb else c statement

7/29/2019 Lecture#2: Introductory Python

16/21

Blocks

Blocks are intended (with spaces, not tabs!)

ifx > y:

print x > y x = y

elifx == y: print X = Y

else: print X < Y

Empty block: pass

7/29/2019 Lecture#2: Introductory Python

17/21

Linebreaks

Break the line:

x = [1, 2, \3,4]

a = Somemultiline

string

x = [1, 2,3,4]

x = (1, 2,

3,4)

x = {a:1,

b:4)

x = {a:1,

b:4)

7/29/2019 Lecture#2: Introductory Python

18/21

Iterations

for i in some_iterable:

do_something(i)

some_iterable:

list, tuple, string, set, other iterable objects

while (x > 5):

do_something(x)

x += 1

7/29/2019 Lecture#2: Introductory Python

19/21

Functions

defmy_func(a, b=None):

print a and b are positional arguments

print b has default value

my_func(1) #the same as my_func(1, None)

my_func(1, 2)

Can have variable number of arguments

7/29/2019 Lecture#2: Introductory Python

20/21

Files

f = open(filename, mode), f.close()mode:

r - read (default),

w - write (existing file is erased),

a - append,

r+ - read and write

f.read() or f.read(size) #read entire file (be careful) or size bytes

f.readline() #read line

Iterate over file:

for line in f:

print line

7/29/2019 Lecture#2: Introductory Python

21/21

Questions?