December 2018 - khemputhea

Friday, December 28, 2018

Python December 28, 2018

Create virtual environments for python with conda

1. Check conda is installed and in your PATH

Open a terminal client.
Enter conda -V into the terminal command line and press enter.
If conda is installed you should see somehting like the following.

$ conda -V
conda 3.7.0

2. Check conda is up to date

In the terminal client enter

conda update conda

Upadate any packages if necessary by typing y to proceed.

3. Create a virtual environment for your project

In the terminal client enter the following where yourenvname is the name you want to call your environment, and replace x.x with the Python version you wish to use. (To see a list of available python versions first, type conda search "^python$" and press enter.)

conda create -n yourenvname python=x.x anaconda

Press y to proceed. This will install the Python version and all the associated anaconda packaged libraries at “path_to_your_anaconda_location/anaconda/envs/yourenvname”

4. Activate your virtual environment.

To activate or switch into your virtual environment, simply type the following where yourenvname is the name you gave to your environement at creation.

source activate yourenvname

Activating a conda environment modifies the PATH and shell variables to point to the specific isolated Python set-up you created. The command prompt will change to indicate which conda environemnt you are currently in by prepending (yourenvname). To see a list of all your environments, use the command conda info -e.

5. Install additional Python packages to a virtual environment.

To install additional packages only to your virtual environment, enter the following command where yourenvname is the name of your environemnt, and [package] is the name of the package you wish to install. Failure to specify “-n yourenvname” will install the package to the root Python installation.

conda install -n yourenvname [package]

6. Deactivate your virtual environment.

To end a session in the current environment, enter the following. There is no need to specify the envname - which ever is currently active will be deactivated, and the PATH and shell variables will be returned to normal.

source deactivate

6. Delete a no longer needed virtual environment

To delete a conda environment, enter the following, where yourenvname is the name of the environment you wish to delete.

conda remove -n yourenvname -all

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Tuesday, December 11, 2018

Python December 11, 2018

The For Loop in Python

A for loop is used for iterating over a sequence

Example :

fruits = ["apple", "banana", "cherry"]
for x in fruits:
print(x)

Note: The for loop does not require an indexing variable to set beforehand.

Looping Through a String

for x in "banana":
print(x)

The break Statement

Exit the loop when x is "apple":

fruits = ["orange", "apple", "cherry"]
for x in fruits:
  print(x)
  if x == "apple":
    break

The continue Statement

With the continue statement we can stop the current iteration of the loop, and continue with the next:

fruits = ["orange", "apple", "cherry"]
for x in fruits:
if x == "apple":
continue

print(x)

The range() Function

To loop through a set of code a specified number of times, we can use the range() function,

The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.

for x in range(6):
print(x)

Else in For Loop

The else keyword in a for loop specifies a block of code to be executed when the loop is finished:

Print all numbers from 0 to 5, and print a message when the loop has ended:

for x in range(6):
print(x)
else:
print("Finally finished!")

Nested Loops

A nested loop is a loop inside a loop.

The "inner loop" will be executed one time for each iteration of the "outer loop":

adj = ["red", "big", "tasty"]
fruits = ["apple", "banana", "cherry"]

for x in adj:
for y in fruits:
print(x, y)

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