Saturday, March 25, 2017

Python Part2: Conditional statements, While loops, Strings and Range

Conditional statements

If expr:
     print("expr is true")

If expr:
     print("It's true")
else:
     print("its’s false")

Python provides the elif keyword to eliminate the need for nested if … else structure.

h = 5
if h > 5:
      print("greater than 5")
elif h < 2:
      print("less than 2")
else:
      print("between 2 and 5.")

While loops

# While loop 
 While expr: 
     print("loop while expr is true") 

# Do-while in python 
 While True: 
     If expr: 
          Break

Strings

  • Immutable sequence of Unicode codepoints.
    • Immutable mean when you construct a string you can't modify its content.
  • Strings with Newlines
    • Multiline strings
      • """ this is
      • Multiline string"""
    • Escape sequences
      • This is \nmultiline \nstring.
  • len(s) gives number of codepoints(characters).
  • The + operator can be used for string concatenation.
    • >>> "This" + "is" + "a" + "string"
    • Thisisastring
  • Strings are immutable, so the += operator re-binds the reference to a new object. 
  • Use sparingly, concatenation with + or += can cause performance degradation. 
  • Call the join() method on the separator string. 
    • >>> Numbers = ';'.join([1, 2, 3, 4]) 
    • '1;2;3;4' 
  • Use the split() to divide a string into a list. 
    • >>> Numbers.split(';') 
    • [1, 2, 3, 4] 
  • Without an argument, split() divides on whitespace.
  • Join()-ing on an empty separator is an important and fast way of concatenating a collection of strings. 
  • The partition() method divides a string into three around a separator: prefix, separator, suffix.
  • Tuple unpacking is useful to destructure the result.

Range

  • Arithmetic progression of integers. 
  • Stop value is one-past-the-end. 
    • >>> range(5) 
    • range(0, 5) 
  • Ranges are 'half open'-start is include but stop is not. 
    • >>> for I in range(5) 
    • print(I) 
    • 4
  • Stop value of a range used as start value of consecutive range. 
    • >>> list(range(5, 10)) 
    • [5, 6, 7, 8, 9] 
    • >>> list(range(10, 15)) 
    • [10, 11, 12, 13, 14] 
  • Optional third step value. 
    • >>> List(range(0, 10, 2)) 
    • [0, 2, 4, 6, 8] 
  • Range(stop) range(10) 
  • Range(start:stop) range(0, 10) 
  • Range(start:stop:step) range(0, 10, 2)

Python Part1: Introduction, Install on windows, Scalar Types and Relational Operators

Introduction to python

  1. Open source programming language developed in late 1980’s.
  2. Strongly typed language in the sense that every object in the language has a definite type.
  3. At the same time, it is dynamically typed means no type checking prior to running it.
  4. General purpose language. 
  5. There are some areas where it's less suitable than others, for example, in extremely time sensitive or memory constrained environments.

Install python on windows

Scalar types

  • Int
  • Float
  • None
  • bool

Relational operators

  • ==      value equality
  • !=       value inequality
  • <        less-than
  • >        greater-than
  • <=      less-than or equal to
  • >=      greater-than or equal to

Sunday, June 26, 2016

How To:Set python virtual environment as python interpreter in eclipse

In this lesson we 'll set virtual env as default interpreter in pydev eclipse project.

1). In PyDev Package Explorer panel, right click on project name and select Properties, a new window will open.

2). Click PyDev - Interpreter/Grammar -> Click here to configure an interpreter not listed, a new window will open.

3). Click PyDev -> Interpreters -> Python Interpreter on left panel.

4). In Python Interpreters section click New -> Browse

5). Open virtual environment folder, move to Scripts folder, select python.exe file and click Open.

6). Enter venv in Interpreter Name: instead of default value and click Ok. You can choose name of your own choice.

7). Select newly added python interpreter iPython Interpreters section and click OK

8). Now select newly added python interpreter under Interpreter drop down list and click OK.

How To:Import python project in eclipse

In this lesson we 'll import python django project in pydev eclipse.
Copy these two files from some existing pydev eclipse project to root folder of new project which you want to import in eclipse.
.project
.pydevproject

Open .project file in notepad and change name to your_project_name.
If you don't have these files then you can create them yourself.


Open notepad, copy following text, click File -> Save As... -> Enter ".project" in File name: -> Select All Files from Save as type: drop down list.


<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>your_project_name</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
<buildCommand>
<name>org.python.pydev.PyDevBuilder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
<natures>
<nature>org.python.pydev.django.djangoNature</nature>
<nature>org.python.pydev.pythonNature</nature>
</natures>
</projectDescription>

Now again open notepad, copy following text, click File -> Save As... -> Enter ".pydevproject" in File name: -> Select All Files from Save as type: drop down list.


<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<?eclipse-pydev version="1.0"?><pydev_project>
<pydev_variables_property name="org.python.pydev.PROJECT_VARIABLE_SUBSTITUTION">
<key>DJANGO_MANAGE_LOCATION</key>
<value>manage.py</value>
</pydev_variables_property>
<pydev_pathproperty name="org.python.pydev.PROJECT_SOURCE_PATH">
<path>/${PROJECT_DIR_NAME}</path>
</pydev_pathproperty>
<pydev_property name="org.python.pydev.PYTHON_PROJECT_VERSION">python 3.0</pydev_property>
<pydev_property name="org.python.pydev.PYTHON_PROJECT_INTERPRETER">Default</pydev_property>
</pydev_project>

Open eclipse, click File -> Import. New window will open. Now select 'Existing Projects into Workspace' under 'General' and click Next. On new window browse to project root directory and select root folder. Then click finish.

Saturday, June 25, 2016

How To:Create virtual python environment and Install pypi packages in window env

In this lesson we 'll create virtual environment for our python project and install all necessary packages from pypi though cmd, which 'll used in our project.

1). Open directory where you want to create virtual environment.

2). Open cmd in same directory by clicking shift + mouse right key and then select 'open command window here'.


3). Install virtual environment by running following command in cmd. If virtual environment already installed then skip this step.


pip install virtualenv

4). Type following command in cmd and press enter. It will create virtual environment. 


virtualenv env

You can see a new folder is added with name env. You can change name of virtual environment to your own choice, just change the env to Your_Own_Name in later part of command.

5). Now type this command in cmd and press enter. Virtual environment will be activated.


env\scripts\activate

You can see (env) in start of line in cmd.

6). Now we 'll install all necessary package from pypi, which 'll be used in our project. Run following commands in cmd.


pip install django
pip install djangorestframework
pip install django-oauth-toolkit
pip install pymysql
pip install pythondbhelper


Now virtual environment is ready with all necessary pypi packages.