Rules
Python relies on proper indentation.
For example:
age = 18
if age >=18:
print("Be sure to vote")
else:
print("Sorry, too young") |
Naming Rules
A variable name: MUST begin with a letter or underscore(_) |
CANNOT contain spaces, punctuation or special characters others than the underscore |
CANNOT begin with a number |
CANNOT be the same as a reserved keyword in Python such as print, True, else, etc |
A variable name is case sensitive |
built-in functions
print() |
this outputs something to the screen |
input() |
ask for input from the program user |
str() |
converts a variable to a string data type |
int() |
convert a variable to an int data type |
float() |
convert a variable to a float(decimal) data type |
round() |
rounds a number |
Comparison Operators
== |
Equal to |
!= |
Not equal to |
> |
Greater than |
< |
Less than |
>= |
Greater than or equal to |
<= |
Less than or equal to |
Basic Math Operators
+ |
Addition |
- |
Subtraction |
* |
Multiplication |
/ |
Division |
% |
division remainder |
** |
Exponent |
Data Types
str |
string(characteres typically words, sentences) |
int |
integer(0,5,133) |
float |
decimal number(1.23,623.664) |
list |
a collection of variables (mango, banana, oranges) |
bool |
boolean value (True, False) |
LOCAL/GLOBAL Variables
LOCAL |
Variable created within a function and only can be used by the function that defines them |
GLOBAL |
Variable defined outside of a function and can be accessed by any function without passing them to the function. Read-only and cannot be modified |
try and except
try:
code statements
except: #for all exceptions
code statements
try:
code statements
except ValueError: #Specific error type
code statements |
|
|
Concatenate using "+" or "f"
combining strings
myName = "Name"
print("Hello " + myName)
print(f"Hello {myName}")
string and a numeric value
age= 22
print("Your age: " + age)
print(f"Your age: {age}") |
Capital and lowercase letters
hello = "hello world"
print(hello.upper())
# will print HELLO WORLD
print(hello.lower())
# will print hello world
print(hello.capitalize())
# will print Hello world
|
Control loops
break |
breaks out of your loop causing the program to move to the next line after the loop |
continue |
while skip this round of the loop and go into the next loop iteration |
Statements
If Statement
if expression:
statements
elif expression:
statements
else:
statements
While Loop
while expression:
statements
For Loop
for var in collection:
statements
Counting For Loop
for i in range(start, end [, step]):
statements
(start is included; end is not) |
if statements
if myAge < 18:
print("Too young") #If TRUE prints this
elif my Age <21:
print("Go ahead") #If TRUE prints this
else:
print("Bye!") #if FALSE prints this
|
While loops
#while loops run as long as, or while, a certain condition is true
while True:
#do something
else:
#do something
#Example:
current_number = 1 #set the first value
#check the value of current_number and see if it is less than or equal to 5
while current_number <=5:
print(current_number) #print out the value of the variable
current_number += 1 #add one to the variable
|
The loop will run again until the current_value variable becomes 6 and then it will stop. Use break and continue to control loop
for loops
colors = ['red', 'green', 'blue']
#colors is a list data type
for color in colors:
#name each individual item color within the colors list so that you can output the individual variable
print(color)
|
write() method example
**Opening in append mode will add the new data to the end of the file"
with open ("filename.txt, "a") as File:
File.write("Hello\n") |
Read methods
read() |
read the entire file and return its contents as a string |
readlines() |
read the entire file and return its contents as a list |
readline() |
read the next line in the file and returns its content as a string |
read() adn readlines() work best for smaller files. readline() for larger files.
|
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Function Definition
Function named blocks of code that are designed to do a specific task
def name(arg1, arg2, ...):
code statements
return expr |
return: stores the variable
It can be with arguments or without it
Functions Example
Function definition with NO arguments/parameters
def helloWorld():
print("Hello, world!")
Function definition WITH arguments/parameters
def helloUser(firstName):
print("Hello", firstName)
Calling a function
helloWorld() |
LISTS/TUPLE
List [ ] |
Collection of items in a particular order. List indexes start at 0 |
Tuple ( ) |
It is a list but Unable to be changed |
Lists functions Example
fruits = |
['apple', 'banana' , 'orange'] |
print(fruits) |
Output an entire list |
print(fruits[2]) |
Output an element in a list: orange |
fruits[0] = 'grapes' |
Modifying an element in a list: apple by grapes |
fruits.append('pear') |
Adding an element to the end of a list |
fruits.insert(0, 'mango') |
adding a list element in a specific position |
fruits.remove('banana') |
removing a list element |
fruits.pop(0) |
removing a specific list element |
fruits.pop() |
removing the last list element |
del fruits |
removing an entire list |
fruits.clear() |
emptying a list |
findApple = (fruits.count("apple")) |
count for specific item |
fruits. reverse() |
reverse the order of list |
fruits.sort() |
sort the list. fruits.sort(key=str.lower) to make sure everything is in lowercase |
sorted_fruits = sorted(fruits) |
If you want the list to remain the same positions, you can use the sorted to create a copy of the sorted list without impacting the original list |
Types of files
Text files |
each line ends with a new line character (\n) or a carriage return character (\r) on Windows systems |
Binary files |
Are intended to be read by other programs, not humans. common types are: program files, image files, audio files, video files, database files and compressed files. |
File fuctions
open(filename, mode) |
mode is an optional argument that specifies how you want to open the file. r = read, a = append, w = write, b = binary. |
filename.close() |
close an open file object |
print(filename.read()) |
output the content of the file |
with open(filename) as newfilename: |
automatically close a file if an exception happens. Also, it allows to assign a name to the file object in the same line of code and ends with a colon: creating a code block |
write() method |
use write mode when you are creating a new file, not when you are working with an existing file of data, Open the file in append mode ("a") if you wish to add to an existing file. |
A file path must be included if the file is not in the same directory as the Python program
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