Python

Installation

Use Anaconda.

• Add C:\Users\[username]\Anaconda3\Scripts to your path
• Run conda init in your bash
• Run conda config --set auto_activate_base false

Usage

How to use Python 3.

pip

Pip is the package manager for python.
Your package requirements should be written to requirements.txt
Install all requirements using pip install -r requirements.txt

Syntax

Ternary Operator

Reference

is_nice = True
state = "nice" if is_nice else "not nice"

Lambda Function

lambda x: x * 2

Strings

String Interpolation

Reference
Python has 3 syntax variations for string interpolation.

name = 'World'
program = 'Python'
print(f'Hello {name}! This is {program}')

print("%s %s" %('Hello','World',))

name = 'world'
program ='python'
print('Hello {name}!This is{program}.'.format(name=name,program=program))

Arrays

Use Numpy to provide array functionality

Array Indexing

Scipy Reference

Lists

The default data structure in Python is lists.
A lot of functional programming can be done with lists

groceries = ["apple", "orange"]

groceries.reverse()
# ["orange", "apple"]

groceries_str = ",".join(groceries)
# "apple,orange"

groceries_str.split(",")
# ["apple", "orange"]

# Note that functions such as map, enumerate, range return enumerable items
# which you can iterate over in a for loop
# You can also convert these to lists by calling list() if necessary

enumerate(groceries)
# [(0, "apple"), (1, "orange")]

Filesystem

Paths

Use os.path

import os.path as path

my_file = path.join("folder_1", "my_great_dataset.tar.gz")
#  "folder_1\\my_great_dataset.tar.gz"

# Get the filename with extension
filename = path.basename(my_file)
# "my_great_dataset.tar.gz"

# Get the filename without extension
filename_no_ext = path.splitext(filename)[0]
# Note that splitext returns ("my_great_dataset.tar", ".gz")

List all files in a folder

Reference

gazeDir = "Gaze_txt_files"
# List of folders in root folder
gazeFolders = [path.join(gazeDir, x) for x in os.listdir(gazeDir)]
# List of files 2 folders down
gazeFiles = [path.join(x, y) for x in gazeFolders for y in os.listdir(x)]

Read/Write entire text file into a list

Reading
[1]

with open('C:/path/numbers.txt') as f:
    lines = f.read().splitlines()

Writing
[2]

with open('your_file.txt', 'w') as f:
    f.write("\n".join(my_list))

Create Directory if it doesn't exist

Reference

# Or os.makedirs(path, exist_ok=True)
def ensure_dir_exists(dir_path):
    if not os.path.exists(dir_path):
        try:
            os.makedirs(dir_path)
        except OSError as exc: # Guard against race condition
            if exc.errno != errno.EEXIST:
                raise


# Example usage to create new_dir folder
ensure_dir_exists("new_dir")
# or
ensure_dir_exists(os.path.dirname("new_dir/my_file.txt"))

Copying or moving a file or folder

Copying
Shutil docs

import shutil

# Copy a file
shutil.copy2('original.txt', 'duplicate.txt')

# Move a file
shutil.move('original.txt', 'my_folder/original.txt')

Regular Expressions (Regex)

Reference

import re
myReg = re.compile(r'height:(\d+)cm')
myMatch = re.match(myReg, "height:33cm");
print(myMatch[1])
# 33

Notes

• re.match will return None if there is no match

Spawning Processes

Use subprocess to spawn other programs.

import subprocess
subprocess.run(["ls", "-l"], cwd="/")

Misc

If you are writing a script with functions you want to be included in other scripts, use __name__ to detect if your script is being run or being imported. What does if __name__ == "__main__" do?

if __name__ == "__main__":

Anaconda

How to use Anaconda:

# Create an environment
conda create -n tf2 python

# Activate an environment
conda activate tf2

# Change version of Python
conda install python=3.6

Libraries

Matplotlib

Main article: Matplotlib

Matplotlib is the main library used for making graphs.
Alternatively, there are also Python bindings for ggplot2
Examples
Gallery