Thread by @Pythonista92

Day 3 of #100DaysOfCode
Python.
Motivation, Don't Repeat Yourself.

1)Defining a function
def function_name(parameters_if_any):
"""indentation identifies the code block of a function"""
return data_if_any

Parameters: are variables in function definition.
Arguments: are the values put into parameters when functions are called.
Calling a function: function_name(arguments_if_any)

2)Modules
These are the codes written to perform useful tasks. Some modules are already part of standard library and others need to be
installed.

-To import an existing module e.g. math
import math #imports whole math module

-To import only a function
from math import pi #only imports pi
-To install a module:
pip install module_name # to get module name refer pypi.org
Some useful modules
string,re,datetime,math,random,os,multiprocessing,subprocess,socket,email,json,sys,doctest

3)Exception Handling:
try:
#do something
except:
#execute this code if exception/error occurs in try block
finally:
#this block will always be executed.
you can specify which exception to handle in except statement.

-Raising an exception:
exceptions can also be raised using raise statements as
Syntax: raise Exception_type("details")
Fun Fact: you can even pass variables or functions as details.

if its the function that is passed
the function will be called(only if an exception has been caused) and do what it is supposed to do then the exception will be raised.
-raise statement when used in except block can be used to determine the type of exception.

-Assertion:
Syntax: assert expression,arguments
here arguments can be int/str,variables, functions just like raise statement.
It can be used as a sanity checker in code.

4)File Handling:
-Opening a file:
f = open("filename","mode")
modes can be:r,w,a,r+,w+,a+(will write about each in details some other day)

-Reading a file:
f.read(n), if n omitted whole file is read, else n number of bytes. returns a string.
f.readlines(n), if n omitted while file is returned as list with each line as a separate element. else n number of lines in list.

-Writing file:
f.write(string_here)

Good Practice:
try:
f=open("filename")
except:
f.close()
5)Data Structures Dictionary:
Syntax:
dic = {key:value,key:value}
key can be any immutable data type.
value can be any data type.

Retrieving data:
dic[key] gives the corresponding value if the key exists else KeyError.
or
dic.get(key) gives the corresponding value if key exists else None.
dic.keys() returns all dictionary keys, in dict_keys data type.

6)Tuples:
Syntax:
tup = (1,'1')
-are immutable data types. But have a look at the following example
tup=(1,[1,2]) its a valid tuple and you can perform all list operations of list e.g tup[1].append(3) gives
tup=(1,[1,2,3])
-tuples are ordered

-can't increase the number of elements in the tuple.
-slicing is the same as that of the list.

Implemented a web scrapper using Selenium.

Machine Learning:
Completed next 3 sections of Machine Learning Crash Course by Google.

#100DaysOfPython #100daysofcodechallenge #100DaysOfMLCode #webscraping