pythonSyntax.md

Syntax Comparison

Hello World

Java:

public class HelloWorld {
    public static void main (String[] args){
        System.out.println("Hello World!");
    }
}

Python:

print("Hello World!")

Single line comments

Java:

//This is a comment

Python:

#This is a comment

Defining variables

Java:

int x = 10;
String y = "Hello";

Python:

x = 10
y = "Hello"
x = "Hello"

(Note the last line which isn't possible in Java)

Boolean expressions

Java:

!(x>0 && y>0) || z > 0

Python:

not(x > 0 and y > 0) or z > 0

Conditionals

Java:

if (a){
  doA();
} else if (b){
  doB();
} else {
  doC();
  doD();
}
doE();

Python:

if a:
  doA()
elif b:
  doB()
else:
  doC()
  doD()
doE()

Note: While the indentation in the Java code is for readability, in Python, incorrect indentation will cause the program to run incorrectly.

Looping

Java:

while (a){
  doA();
}

Python:

while a:
  doA()

Java:

for (int number: listOfNumbers){
  doThing(number);
}

Python:

for number in listOfNumbers:
  doThing(number)

Java:

for (int i = 0; i < 100; i++){
  doThing(i);
}

Python:

for i in range(0,100):
  doThing(i)

Functions

Java:

public int increment(int i){
  return i + 1;
}

Python:

def increment(i):
  return i + 1

Lists:

Lists are the equivalent of Arrays or ArrayLists in Java. However, they can hold different types, and have many inbuilt functions.

An empty list:

myList = []

A prepopulated list:

myList = [1, 2.0, "Hello World!"]

(Note: >>> is used to denote output.)

Getting an item:

myList = [1, 2.0, "Hello World!"]
print(myList[0])
>>> 1

Negative indexes count from the end:

myList = [1, 2.0, "Hello World!"]
print(myList[-1])
>>> "Hello World!"

(You can use both positive and negative indexes on Strings too, to treat them as char arrays!)

Changing an item:

myList = [1, 2.0, "Hello World!"]
print(myList)
>>> [1, 2.0, 'Hello World!']
myList[0] = 5
print(myList)
>>> [5, 2.0, 'Hello World!']

Appending an item:

myList = [1, 2.0, "Hello World!"]
myList.append(1)
print(myList)
>>> [1, 2.0, 'Hello World!', 1]

Helpful links

Lists a lot of Python syntax, starting from most common to least common: https://learnxinyminutes.com/docs/python3/

Comparison between C++ and Python syntax, might be useful: http://jasonpark.me/DuoCoder/public/learn.html?lang_from=cpp&lang_to=py