Python basics
str
string/ text data
await keyword
used in asynchronous functions to specify a point in the function where control is given back to the event loop for other functions to run.
del statement
used to delete objects/variables.
Iterative Keywords
for, while, break, continue, else for: Using for loop, we can iterate any sequence or iterable variable. The sequence can be string, list, dictionary, set, or tuple. while: The while loop repeatedly executes a code block while a particular condition is true
Conditional Keywords
if, elif, else condition keywords act depending on whether a given condition is true or false
frozenset
immutable version of set create using class forzenset()
Import Keywords
import, from, as
Identity operators
is, is not
print(x[5:]
omitting the end_index prints list to end
print(x[:5]
omitting the start_index starts slice at 0
tuple
ordered collections of elements that are unchangeable tuples are immutable a tuple is a read-only version of the list. create a tuple 2 ways Enclosing elements in the parenthesis () Using a tuple() class.
Explicit casting
performed by the user using built-in functions.
pass keyword
performs no operation except to act as a placeholder for a required statement
strip()
removes any whitespace from the beginning or the end
replace()
replaces a string with another string
bytes
represents a group of byte numbers just like an array. bytes are immutable allowed values are 0 to 256
Returning Keywords
return, yield
is operator
returns Boolean True or False. It returns True if the memory address's first value is equal to the second value. Otherwise, it returns False
is not operator
returns boolean values either True or False. It returns True if the first value is not equal to the second value. Otherwise, it returns False.
factorial() math.factorial(x)
returns x factorial
floor()
round a number DOWN to the nearest integer value
ceil()
round the number UP to the nearest integer value
bytearray
same as the bytes type except bytearray mutable bytearray() constructor returns a bytearray object.
for statement
statement that directs program flow through a group of statements a fixed number of times
complex
store complex numbers (real and imaginary part)
python #
symbol to start writing a comment
python indentation
tells a Python interpreter that the group of statements belongs to a particular block of code. The indentation makes the code look neat, clean, and more readable.
try statement
the statement used to enclose code that may contain an exception.
Multi-Line Comments
there is no separate way to write a multi-line comment can use parentheses or \ to continue comments over multiple lines
End of python statement
token \n start new line
trunc()
truncate a number to its nearest integer
Exception-Handling Keywords
try, except, raise, finally, else, assert
if statement
a control flow statement that will execute statements under it if the condition is true. Also kown as a conditional statement.
yield keyword
a keyword that is used like return, except the function will return a generator
python variable
a reserved memory area (memory address) to store value.
code block
a series of statements that are grouped together
string
a set of characters represented in quotation marks
Local variable
a variable that is accessible inside a block of code only where it is declared If we declare a variable inside a method, the scope of the local variable is limited to the method only. So it is not accessible from outside of the method. If we try to access it, we will get an error.
+=
a+=5 Add 5 to a and assign it as a new value to a a = a+5
fabs(x)
absolute value of x
list
an ordered collection (also known as a sequence of elements. List elements can be accessed, iterated, and removed according to the order they inserted at the creation time. Lists are mutable The list can contain data of all data types such as int, float, string Duplicates elements are allowed in the list create a list two ways Enclosing elements in the square brackets []. Using a list() class.
set
an unordered collection of data items that are unique A set is a collection of elements (Or objects) that contains no duplicate elements. Set is mutable Heterogeneous (values of all data types) elements are allowed Insertion order of elements is not preserved, so we can't perform indexing on a Set create a set 2 ways By enclosing values in the curly brackets {} Using a set() class.
Operator Keywords
and, or, not, in, is logical and keyword returns True if both expressions are True logical or keyword returns a boolean True if one expression is true, and it returns False if both values are false logical not keyword returns boolean True if the expression is false
Asynchronous Programming Keywords
async, await
Implicit casting
automatic conversion of data to a different type
Single-line comments
begin with #, interpreter ignores anything written after the # sign, and it is effective till the end of the line.
Transfer Keywords
break, continue, pass transfer keywords are used to alter the program's way of execution in a certain manner
type() method
built-in Python method that checks variable type
break statement
causes an immediate exit of the loop
Inline Comments
concise comments on the same line as the code they describe
Python compound statements
contain (groups of) other statements; they affect or control the execution of those other statements in some way. The compound statement includes the conditional and loop statement.
radians()
convert the angle in degrees to radians
degrees()
convert the angle in radians to degrees
lower()
converts a string to lowercase
upper()
converts a string to uppercase
Structure Keywords
def, class, with, as, pass, lambda
Variable Handling Keywords
del, global, nonlocal
Docstring Comments
describe Python classes, functions, constructors, and methods. The docstring comment should appear just after the declaration. Conventions for writing good documentation strings are mentioned in PEP 257 Triple double quotation marks The docstring comment should appear just after the declaration. A docstring can be a single line or a multi-line comment. Docstring should begin with a capital letter and end with a period.
Variable Scope
dictates what portions of the code can "see" or use a variable, typically derived from where the variable was first created. (See Global v. Local)
4 types of Python statments
1. Print statements 2. Assignment Statements 3. Conditional Statements 4. Looping Statements
Separate multiple statements
;
int
A Python data type that holds positive and negative whole numbers
float
A native type representing rational numbers to limited precision.
return statement
A statement of the form return <expression> It is placed at the end of a function to return a value
continue statement
A statement that causes the remainder of the current iteration of a loop to be skipped. The flow of execution goes back to the top of the loop, evaluates the condition, and if this is true the next iteration of the loop will begin.
Global variable
A variable whose scope is "global" to the program, it can be used and updated by any part of the code. Its global scope is typically derived from the variable being declared (created) outside of any function, object, or method.
bool
A variable whose value can be either true or false is of this data type.
mutable variable
A variable whose value can change after it has been declared
immutable variable
A variable whose value cannot change after it has been declared
casting
Converting from one data type to another
membership operators
In and Not In
Not in operator
It returns True if the object is not present in a given sequence. Otherwise, it returns False
Membership Operator (IN)
It returns a result as True if it finds a given object in the sequence. Otherwise, it returns False.
class keyword
Keyword used to define a class; by default members are private.
tuple packing
Packing can be used when we want to collect multiple values in a single variable
Python keywords
Protected, special words (tells Python you are about to define a function) 36 keywords use keyword module or help() function to get list of keywords All the keywords except, True, False, and None, must be written in a lowercase alphabet symbol.
isinstance
The function call isinstance(ob,C) returns True if object ob is an instance of class C. This is different than testing the type of an object, as it will return True even if the type of ob is a subclass of C.
list slicing
Way to access elements list[start_index : end_index : step] -step = count by __'s -any term can be omitted, will be set to default - a negative step progresses through list backwards
Bitwise Operators
are used to manipulate the individual bits of values.
pass statement
The pass statement does nothing. It can be used when a statement is required syntactically but the program requires no action. Odd as it seems, pass has its uses: 1. It can be used to test a statement (say, opening a file or iterating through a collection) just to see if it works. You don't want to do anything as a result, just see if the statement is correct. 2. More interestingly, you can use pass as a place holder. You need to do something at this point, but you don't know what yet. You place a pass at that point and come back later to fill in the details.
while statements
The while loop statement repeatedly executes a code block while a particular condition is true. Also known as a looping statement.
Logical and
True if both the operands are True
Logical or
True if either of the operands is True
Logical not
True if the operand is False
Value Keyword
True, False, None
with statement
Used to cleanup code for a group of statements, while the with statement allows the execution of initialization and finalization code around a block of code.
return keyword
Used to return a value from a function
dict
unordered collections of unique values stored in (Key-Value) pairs. duplicate keys are not allowed, but the value can be duplicated. heterogeneous (i.e., str, list, tuple) elements are allowed for both key and value in a dictionary. But an object can only be a key in a dictionary if it is hashable. dictionary is mutable Dictionary is unordered so we can't perform indexing and slicing create a dictionary 2 ways Enclosing key:values in the curly brackets {} Using a dict() class.
nonlocal keyword
used in nested functions whose local scope is not defined. This means that the variable can be neither in the local nor the global scope.
Expression statements
used to compute and write a value. An expression statement evaluates the expression list and calculates the value. An expression is a combination of values, variables, and operators.
memoryview
used to create a view of the internal data of an object without copying it
global keyword
used to declare the global variable. A global variable is a variable that is defined outside of the method (block of code). That is accessible anywhere in the code file.
def keyword
used to define user-defined funtion or methods of a class
del keyword
used to delete the object.
import statement
used to import modules.
import keyword
used to import the whole module
Block Comments
used to provide descriptions of files, classes, and functions. Should add block comments at the beginning of each file and before each method.
with keyword
used when working with unmanaged resources (like file streams). It allows you to ensure that a resource is "cleaned up" when the code that uses it finishes running, even if exceptions are thrown.
async keyword
used with def to define an asynchronous function, or coroutine.
Implicit continuation
using parenthesis to write a multi-line statement