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Python-Basics.md

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Variable Assignment

  • Integers
int_variable = 10
  • Floats
float_variable = 1.25
  • Booleans
boolean_variable = True
  • Strings
string_variable = "Hello World!"

Referencing and Printing

  • Print variable values
print(int_variable)
print(float_variable)
print(boolean_variable)
print(string_variable)
  • Print variable types
print(type(int_variable))
print(type(float_variable))
print(type(boolean_variable))
print(type(string_variable))
  • Arithmetic Operation
count = 10 + 2
print(count)
  • String Concatenation
hello = "Hello " + "World!"
print(hello)
  • String Conversion and Concatenation
age = 27
words = "I am currently "
completeSentence = words + str(age)
print(completeSentence)

User Input

  • input() function requests user input from the command line.
  • The user's response is stored as the variable value.
name = input("What is your name? ")
print("Hello " + name)
  • User inputs are received as strings.
  • They must be converted into integers or floats if we intend to do arithmetic.
number = input("Please enter a number to multiply by 2: ")
print(int(number) * 2)

Working with Files

Reading Text Files

  • Method 1
# The open() function creates a connection to an external file
# The parameter passed into the function is the relative or absolute path to file to open
sample_txt_file = open("Sample.txt","r")

# Using the .read() function then stringifies the file's contents
sampleText = sample_txt_file.read()
print(sampleText)

# Closing the connection to the external file in order to save memory
sample_txt_file.close()
  • Method 2: By using context manager, "with" keyword, users are able to work with files from within the blocks. Once users exit the block, the files are automatically closed.
	with open('Sample.txt','r') as sample_txt_file:
		# do something with the file

Writing Text Files

# The open() function is also used for writing, though it defaults to "r"ead
# so we have to use the "w" mode as the second argument ("w"rite, instead of "r"ead)
diary_file = open("MyPersonalDiary.txt", "w")


# The .write() function is then used to push the text into the external file
diary_file.write("I don't write in diaries.")

# Since no spacing or newlines are added between .write() functions, they have to be programmed into the application manually
diary_file.write("\nPeriod.")

Appending Text

# The "a" mode stands for append and allows the application to add new text onto the end of an existing file
notesFile = open("Notes.txt", "a")

# The .write() method in conjunction with the append mode will write to the end of a file
notesFile.write("\nThis is a completely new line of text created by the APPEND mode.")

# Closing the file
notesFile.close()

Strings Method

# Since the file is now a string, it can be modified and worked with using some string functions
# The split() function breaks a string apart into a list based upon common words/characters that appear in the original string
sampleSplit = sampleText.split(" ")

# Since the string was split on spaces, individual words will now be printed when referenced
print(sampleSplit[0])
print(sampleSplit[1])
print(sampleSplit[2])
print(sampleSplit[3]) 
print("-----------")

# The find() function will navigate through some text, determine whether or not the string passed into it is contained within, and return the index of that string
print(sampleText.find("malarkey"))

# This can be exceptionally useful when checking to see if a file contains some specific keywords
if sampleText.find("malarkey") > -1:
    print("Malarkey found!")

if sampleText.find("juice") > -1:
    print("Juice found")

Reading CSV Files

#################################################

Method 1 (Old): Plain Reading (no module)

#################################################

# Connect to the file and read in the text it contains
wrestling_csv = open("WWE-Data-2016.csv", "r")
wrestling_text = wrestling_csv.read()

# Since a CSV is broken into rows and columns, it will need to be split twice
# The first split is to break the original text into rows by splitting on each new line
wrestling_rows = wrestling_text.split("\n")
print(wrestling_rows[0])
print(wrestling_rows[1])
print(wrestling_rows[2])
print(wrestling_rows[3])
print("-----------")


# The next split will then split the row into its respective columns on commas
wrestling_cells = wrestling_rows[0].split(",")
print(wrestling_cells[0])
print(wrestling_cells[1])
print(wrestling_cells[2])
print(wrestling_cells[3])

###################################################

Method 2: Improved Reading using CSV module

###################################################

import csv

csvFile = open("WWE-Data.csv")

# The `csv.reader()` method is used to read in the data within the file
contents = csv.reader(csvFile)
# Contents returned as a CSV object
print(contents)

# The CSV object can be looped through without any splitting
for row in contents:
    print(row)

    # rows are already created as lists of cells for us, so no need to split
    print(row[0])

OS Module

# import the os library to use later
import os

# The os.path.join() function creates a file path which will work for the current file system (so this code will work for any filesystem)
real_path = os.path.join("Resources", "CoolText.txt")

# This path can then be used for open()
cool_text = open(real_path)
print(cool_text.read())
print("--------------")


# The os.path.isfile() function returns True if the file path provided points to an actual file, false otherwise
fake_path = os.path.join("Resources", "NotAFile.txt")
print(os.path.isfile(real_path))
print(os.path.isfile(fake_path))
print("--------------")


# you can use isfile before you do a read to avoid errors if you're not sure the file will be there:
fileName = input("Please enter the file you're looking for: ")

filePath = os.path.join("Resources", fileName)

if os.path.isfile(filePath):
    print("Found it!")
    # read the file here
else:
    print("That file doesn't exist")

##############

OSWalk

##############

# import the os library to use later
import os

folder_path = os.path.join("Resources", "DiaryEntries")

# The os.walk() function is used to navigate through a collection of folders/files
# This function returns three values for each step it takes: root, dirs, and files
for root, dirs, files in os.walk(folder_path):

    # The root is the folder that is currently being searched through
    print("Currently inside of... " + root)

    # The dirs list stores all of the names of the folders inside the current root
    print("The folders in here are..." + str(dirs))

    # The files list stores all of the names of the files inside the current root
    print("The files in here are..." + str(files))
    print("~~~~~~~~~~")

print("--------------")

# In order to construct the file path to use dynamically...
for root, dirs, files in os.walk("Resources"):

    # Loop through all of the files in the current root
    for file_name in files:

        # Create a path by combining (joining) the root and the file name
        current_file_path = os.path.join(root, file_name)
        print(current_file_path)

        # We can then check that the file exists through using os.path.isfile()
        print("EXISTS: " + str(os.path.isfile(current_file_path)))

Zip Module

import zipfile

# Create a reference to the ZIP file you would like to extract
zipfileReference = zipfile.ZipFile("Text.zip")

# Run the `.extractall()` function on the variable containing the connection to the external ZIP file
zipfileReference.extractall()

# creating another reference, this time to a locked ZIP file
lockedZip = zipfile.ZipFile("Books.zip")

# Variable used to store the password string
password = "password"

# Running the `.extractall()` function with a password
lockedZip.extractall(pwd=password.encode('cp850','replace'))

List

  • Create a list and save it to a variable
hobbies = ["Rock Climbing", "Bug Collecting", "Cooking", "Knitting", "Writing"]
print(hobbies)
  • Select the first and second values from the list
print(hobbies[0])
print(hobbies[1])
  • len() tells us how long the list is (5)
print(len(hobbies))
  • Use index() to find the index of a specific value in a list
print(hobbies.index("Cooking"))
  • Use append() to add values to the end of the list
hobbies.append("Gaming")
print(hobbies)
  • Use remove() to remove values from the list
hobbies.remove("Bug Collecting")
print(hobbies)

Dictionary

  • Unlike lists, dictionaries store information in pairs

    • A list of actor's names
    actors = ["Tom Cruise",
     "Angelina Jolie",
     "Kristen Stewart",
     "Denzel Washington"]
    • A dictionary of an actor
    actor = {"name": "Tom Cruise"}
print(actor["name"])

  • A dictionary can contain multiple pairs of information

actress = {
  "name": "Angelina Jolie",
  "genre": "Action",
  "nationality": "United States"
  }
  • A dictionary can contain multiple types of information
another_actor = {
    "name": "Sylvester Stallone",
    "age": 62,
    "married": True,
    "best movies": [
      "Rocky",
      "Rocky 2",
      "Rocky 3"
      ]
    }

print(another_actor["name"] + " was in " + another_actor["best movies"][0])
  • A dictionary can even contain another dictionary
film = {"title": "Interstellar",
        "revenues": {
          "United States": 360, 
          "China": 250, 
          "United Kingdom": 73
          }
        }

print(film["title"] + " made " + film["revenues"]["United States"] + " in the US.")