you can write a comment strings in your code, they will not be considered as code to execute, rather than a good practice hinting and describing near code
# this is a comment, on line
"""
comment in few lines
do nothing, but inform
"""
EXPRESSION is programming language construction, which consists of other EXPRESSIONS or can contain other VALUES , VARIABLES, FUNCTIONS CALLS connected with **OPERATORS (+,-,=,*) **
# simple expression
# 2 is a value or integer constant , then arithmetic operator + , than again integer 2 (constant)
2 + 2
# more complex like algebra
999.2 * ( 2 + 5 ) / 5
One of the most important and simple operator in imperative languages (like Python, C, C#...)
# look at this assignment expression
user = "FancyBeard"
# make the name (variable) 'user' contains (points) to string 'FancyBeard'
# now variable with name 'user' contains "FancyBeard"
In common scenarios syntax is kinda following:
NAME_TOSAVE_THERESULT = EXPRESSION_TO_CALCULATE_LEFT_PART
## арифметические операторы +, -, /, *
# sum is a variable
# 7+2 is an language expression
sum = 7 + 2
x = 10 * 5 + 4 / 3 - 1.5
## скобки определяют порядок выч-я как в математике
x = 10 * (5 + 4 / 3 - 1.5)
## Именна переменных зависят от регистра, могут начинаться с _ или букв
1a ## wrong, нельзя начинать с имя переменной с числа
= a1 ## wrong, должен быть правый операнд (переменная)
_1a = 1 ## ok
x,y,z = 99,-1,"20"
a = b = c = 0x2199 # hexademical
a1,b1,c1 = "WOW"
a, *b, c = "Python"
a # P
b # ['y', 't', 'h', 'o']
c # n
# сокращённая форма a = a + "Django"
a += "Django"
print(a,b,c)
Just look what error message Python interpreter showed after failure running the program. Message will get you:
- NAME of error
- SHORT DESCRIPTION
- most important the NUMBER OF LINE in which it happened
usually some stupid grammer mistake in written code (not logical)
if you try to use a name (variable) in function, or other code before you've assign it
z = 999
print(zz)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'zz' is not defined
You try to get element from collection by index which is not exists
# you define the name (variable) a as a list structure with two elements 1,2
a = [1,2]
# now you try to get element with index 3 (which is actually the 4rt element)
a[3]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: list index out of range
Pretty self talking
not_possible = 1 / 0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero
name = "Ola"
# string concatenation
both_values = "s1" + "s2"
f = 1.5
f2 = 10/3
he_is_old = True
# new age
age = 16
if age < 35:
he_is_old = False
# examples useful simple functions
- len()
- type()
- str()
- int()
- float()
multiline_str =
"""
string for
2 lines
"""
# pass - ничего не делать, как заготовку можно
def function_stub():
pass
# всегда возвращает True
def true_function():
return True
# how to call function
function_stub()
yes = true_function()
"My name is %s, age %d".format() % name,age
#checks if two values are equal
5 == 5 # True
#checks if two values are not equal
6 != 5 # True
#checks if first value is less than second
5 < 2 # False
#checks if first value is greater than second
3 > 5 # True
#checks if first value is greater than or equal to second
1 >= 1 # True
#checks if first value is less than or equal to second
99 >= 100 # False# составные условия
if (name=="Dee" and age < 40):
print("Alright")
else:
print("wrong...")
(a>5 or a<2) and b==10
- lists - mutable ordered
- strings - immutable ordered
- tuple - immutable unordered
- dictionary - mutable unordered
- set - mutable unordered
for item in COLLECTION:
do_something(item)
# print five times the string
for item in range(1,5):
print("five lines")
- Modules can be imported in three different ways:
import module
from module import functions
from module import *
import math
import random
random.randint(10,44)
math.sqrt(5)
# enter this in REPL console to get Python keywords
help("keywords")here is a list of the python keywords
REMEMBER THEM! AND DONT USE AS NAMES
False class from or
None continue global pass
True def if raise
and del import return
as elif in try
assert else is while
async except lambda with
await finally nonlocal yield
break for not
empty = { }
# try:
code()
# except:
print('Error')
# python package manager
> pip install requests
- create, open, read, write, append, delete
- CSVFile module
while expression:
pass
# useful builtin functions
range(1,5)
sum([1,2])
sum("1","2") # wrong
sum(["1","2"]) # wrong types
# the same
# min,max
GET ALL BUILTIN OBJECTS IN CURRENT MODULE
> dir(__builtins__)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExistsError', 'FileNotFoundError', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError', 'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'ModuleNotFoundError', 'NameError', 'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError', 'RecursionError', 'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopAsyncIteration', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '__build_class__', '__debug__', '__doc__', '__import__', '__loader__', '__name__', '__package__', '__spec__', 'abs', 'all', 'any', 'ascii', 'bin', 'bool', 'breakpoint', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip']
# What is class (template for a data type - your own)
# how to create a class and instantiate an object
# class variables
# class methods
#constructor method - inheritance (parent,child class)
- Polymorphism - redefining methods in child classes
map, reduce list comprehensions
- ipython3 - fancy REPL
- PyCharm amazing for IDE for web, big projects, etc
- Spider IDE - i think it's bettet for education
- Anaconda distribution - is nice all in one solution with libs and packages, and more for la Pythonista
Let me try to explain how it works step by step for those who aren't familiar with programming
In a simplifed way. it can also be applied to the assigment expression in other popular imperative languages - JavaScript, C/C++/C#, BASIC, Pascal. In computer reality, high-level programming languages, usually can do a lots of stuff between one expression, and C/C++/C# are languages with *strong static typisation * )) dont bother now
# SO at the LEFT we define the name (variable)
# which will recieve the result of expression from RIGHT PART-
lets pretend to calcluate the working hours in a year -
business_hours is the NAME also called VARIABLE, which should contain the result after calculation
RIGHT PART
-
so we can make an arithmetic expressions
5(days in week) multiply by365(in year) -
also we need number of hours in day, in this example there is a special function which will return number of hours in day
-
this function has a name
get_working_hours_per_day -
to get a result (call a function) the Python syntax is the NAME_OF_THE_FUNCTION() **with brackets ** , in our case get_working_hours_per_day()
-
we have all the data (numbers) to make our simple calculation, so we can compose an expression
5 * 365 * 365 get_working_hours_per_day() -
we can run this expression in Python console , (we suppose that this function already exists), and will get the result of this expression, it should be a number , a decimal (integer). We got the RESULT we needed.
-
Now we need to store it (place it, assign it) to a name working_hours
-
we need to use assigment operator - the
=character -
on the left we place our name to store result , than =, and on the right the whole expression with numbers and function call
working_hours = 5 * 365 * get_working_hours_per_day()
If you a newbie and you want to read this in verbal language - you can smth like
working_hours will be equal to 5 multiply by 365 multiply by the result of this get_working_hours_per_day function calculation
working_hours = 5 * 365 * get_working_hours_per_day()
RIGHT PART from the = sign (assigment operator to call it right) is now an expression
We ASSIGN (in simple connect the LEFT_PART to the name in RIGHT_PART via = operator) , LEFT_NAME = RIGHT_EXPRESSION - can be called an assigment
Totoally now we got "our complicated" expression, which consists of other expressions and language constructs. In programming such language constructs and expressions, can be very tricky and "not plain and obvious")
We can run it , the programming language (interpreatator) will do some checks at first (is a function with this name exists, can we call it, than it start to solve - multiply the values in a LEFT_PART )
Order of execution and computation probably in this scenario should be:
-
the call to function with name get_working_hours_per_day() returning a number ( calling a function sometimes means just simple go to her inner code and parse and computate - execute, complete the inner code in function, and if function returns the result, to get it back on level 1)
-
so result from function for example 30
-
now python make the RIGHT_PART as an expression similar like this
5 * 365 * 30 -
its plain simple math , it will be easy evauluated to a decimal number 9750
-
Well on this step out inner representation of whole expression became
working_hours = 9750 -
well the Python should probably create a name working_hours, asks for little memory to store the pointer to the value (not value itself), to place it in a kinda special inner table with variables, and numer 9750 (is already a pointer to a memory where an number object 9750 holds), so python probably will just assign the pointer of 9750 to the new name