Syntax Comparison: Swift vs Python

11 min readApr 10, 2020

Sharing my notes that I prepared to remember the python syntax from already known language syntax. (Swift 4.2; Python 3.7)

“The Loci method is one of the most ancient memorization tools known, and is based on attaching individual items you need to remember, to individual points on a route you are familiar with, so you can easily recall the items as you “walk” that route in your mind.”

Basics
Collection Types
Class, Struct
Closures
Exception Handling
Unit Testing

Import Modules

Swift

import Foundation

typealias a module

typealias SMSomeStruct = SomeModule.SomeStruct

Import only parts from a module

import struct SomeModule.SomeStruct
import class SomeModule.SomeClass
import func SomeModule.someFunc

Python

import calculator

typealias a module

import calculator as calc

Import only parts from a module

from calculator import multiply# usage
result = multiply(2, 4)

Constants

Swift

let maximumHeight = 50

Python

Create constant.py file (global file)

PI = 3.14
GRAVITY = 9.8
MAXIMUM_HEIGHT = 50

Usage:

import constantconstant.MAXIMUM_HEIGHT

Variables

Swift

var userName = "Sit Bibendum"
userName = "Malesuada Mollis"

Python

userName = "Sit Bibendum"
userName = "Malesuada Mollis"# Assigning multiple values to multiple variables
a, b, c = 5, 3.2, "Hello"# to assign the same value to multiple variables at once
x = y = z = 1000

Comments

Swift

// single comment/* multi line comment */

Python

# python comment, no multiline comment

Print

Swift

let id = 525
let name = "Porta Tortor"print(id, name)		                // 525 Porta Tortor
print(id, name, separator: ", ")	// 525, Porta Tortor

Python

id = 525
name = "Porta Tortor"print(id, name)		        # 525 Porta Tortor
print(id, name, sep=', ')	# 525, Porta Tortor

Print Terminator Usage

Swift

for i in 1 ..< 10 {
    print(i, terminator: " ")
    if i % 3 == 0 {
        print()
    }
}output: 1 2 3 4 5 6 7 8 9

Python

for i in range(1, 10):
  print(i, end=' ')
  if i % 3 == 0:
      print()output: 1 2 3 4 5 6 7 8 9

Multiline Strings

Swift

let html =
"""
<html>
    <body>  </body>
</html>
"""

Python

html = """
<html>
    <body>  </body>
</html>
"""

(or) using single quotes

html2 = '''
<html>
    <body>  </body>
</html>
'''

String Interpolation

Swift

let id = 525
let name = "Porta Tortor"let msg = "\(id): \(name)"      // 525: Porta Tortor

Python

id = 525
name = "Porta Tortor"msg = "%d: %s" % (id, name)                     # 525: Porta Tortormsg = "{}: {}".format(id, name)			# 525: Porta Tortormsg = "{0}: {1}".format(id, name)		# 525: Porta Tortor

String Concatenation

Swift

let userID = 525
let firstName = "Cursus"
let lastName = "Dolor"let text = firstName + " " + lastName + " (" + String(userID) + ")."output: Cursus Dolor (525).

Python

userID = 525
firstName = "Cursus"
lastName = "Dolor"text = firstName + " " + lastName + " (" + str(userID) + ")."output: Cursus Dolor (525).

How to get object type ?

Swift

let height = 5.7
type(of: height)	 // Double.Typeif height is Int {
    // ..
}

Python

height = 5.7
type(height) 		# <type 'float'>if (type(height) is float):
    # ..

String to Int

Swift

let userIDString = "525"
let userID = Int(userIDString)

Python

user_id_string = "525"
user_id = int(user_id_string)

Binary to Number

Swift

let binary = "11001"
let number = Int(binary, radix: 2)		// 25

Python

binary = "11001"
number = int(binary,2)                         // 25

Boolean

Swift

var isEnabled = true           // false

Python

isEnabled = True   		# False

Tuples

Swift

let http404Error = (404, "Not Found")let code = http404Error.0
let message = http404Error.1
// or
let (statusCode, statusMessage) = http404Error

Python

http404Error = (404, "Not Found")code = http404Error[0]
message = http404Error[1]

Nil, None

Swift

var email: String? = nil

Python

email = None

del Statement

Swift

// ??

Python

name = Mattis Ridiculus
del name 		# object will be deleted completly
print(name) 		# NameError: "name 'name' is not defined"

If Statement

Swift

var email: String? = nil// Optional wrap
if let email = email {
    print(email)
} else {
    print("n/a")				
}// Force unwrap
if email != nil {
    print(email!)
} else {
    print("n/a")
}Output: n/a

Python

email = Noneif email is not None:
    print(email)
else:
    print("n/a")

if email != None:
    print(email)
else:
    print("n/a")
    
Output: n/a

If with Multiple Conditions

Swift

if self.x == other.x && self.y == other.y {
    return true
} else {
    return false
}

Python

if (self.x == other.x and self.y == other.y):
    return True
else:
    return False

Escape characters

Swift

let text = "one\ntwo\nthree"let regExp = "Language: \"Swift\", version: \"4.2\""

Python

text = "one\ntwo\nthree"regExp = "Language: \"Python\", version: \"3.7\""# one two three
# Language: "Python", version: "3.7"

Counting Characters

Swift

let text = "abc 123"
text.count					// 7

Python

text = "abc 123"
len(text)					# 7

Enum

Swift

enum Color: Int {
    case red = 1
    case green
    case blue
    
    var name: String {
        switch self {
        case .red:
            return "red"
        case .green:
            return "green"
        case .blue:
            return "blue"
        }
    }
}// Usage:
Color.green
Color.green.name
Color.green.rawValuelet selectedColor = Color.greenif case Color.green = selectedColor {
    print("Selected right color")
} else {
    print("Wrong color selected \(selectedColor.name)")
}

Python

from enum import Enumclass Color(Enum):
    red = 1
    green = 2
    blue = 3
    
Color.green                     # Color.green
Color.green.name		# green
Color.green.value		# 2# Usage:
selectedColor = Color.greenif selectedColor is Color.green:
    print("Selected Right color")
else:
    print("Wrong color selected: {}".format(selectedColor.name))

Switch

Swift

switch input {
     case 0:
         //..
     case 1:
         break
     case 2:
         //..
}

Python

python does not have any switch case statement. 
Alternatively we use dictionary mapping.

Pass by reference

Swift

func swapInts(a: inout Int, b: inout Int) {
    let temp = a
    a = b
    b = temp
}var a = 50
var b = 100
swapInts(a: &a, b: &b)
print(a, b)

Python

There are no variables in Python. There are names and objects in - Python and together they appear like variables

Decorators

Swift

// TODO: ??

Python

def validateInputs(input_function):
    def validation(a, b):
        if b == 0:
            print("Can't divide by 0")
            return
        return input_function(a, b)    # call input function
    return validation
@validateInputs
def div(a, b):
    return a / bdiv(10,0)# need to check how to achieve Decorator Pattern using python decorators. (ie.. without modifying the source code file)

Yield (instead of return), Next

Swift

// achieve using closures
func makeIncrementer(_ amount: Int) -> () -> Int {
    var runningTotal = 0    func incrementer() -> Int {
        runningTotal += amount
        return runningTotal
    }
    return incrementer
}let incrementByTen = makeIncrementer(10)
incrementByTen()
incrementByTen()for _ in 0..<10 {
    print(incrementByTen())
}

Python

def makeIncrementer(amount):
    runningTotal = 0
    while True:
        runningTotal  += amount
        yield runningTotal
        
incrementerByTen = makeIncrementer(10)
next(incrementerByTen)			# 10
next(incrementerByTen)			# 20for i in range(10):
    print(next(incrementerByTen))       # 30 40 ... 120

Collection Types

Array

Array Operations

Swift

var hetro: [Any] = ["one", 10, 2.5]hetro[0]
// Negative Indexing not allowedhetro[1] = "100"hetro.remove(at: 0)hetro.append("five")
hetro.append(4.9)
hetro.append("five")// No inbuilt method to remove an element directlyhetro.insert(10000, at: 1)

Python

hetro = ["one", 10, 2.5]hetro[0]     # one
# reverse index
hetro[-1]    # 2.5
hetro[-2]    # 10hetro[1] = "100"# pop at index
hetro.pop(0)# append
hetro.append("five")				
hetro.append(4.9)
hetro.append("five")# remove first occurances
hetro.remove("five")# insert at index
hetro.insert(1, "100000")

Empty array

Swift

var list = [Any]()

Python

list = []

Multidimensional arrays

Swift

let matrix = [[1,2,3], [4,5,6], [7,8,9]]
matrix[0][0]
matrix[2][2]

Python

matrix = [[1,2,3], [4,5,6], [7,8,9]]
matrix[0][0]								
matrix[2][2]

Array Length

Swift

let list = ["zero", "one", "two", "three", "four"]
list.count

Python

list = ["zero", "one", "two", "three", "four"]
len(list)

Array Slicing

Swift

let list = ["zero", "one", "two", "three", "four"]list[1...4]
list[..<2]
list[2...]

Python

list = ["zero", "one", "two", "three", "four"]list[1:4]    # ['one', 'two', 'three']
list[ :2]    # ['zero', 'one']
list[2: ]    # ['two', 'three', 'four']

list[start: end-1] understanding-pythons-slice-notation

Array with a Default Value

Swift

var countArray = Array(repeating: 0, count: 10)		
// [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Python

countArray = [0] * 10
# or
countArray = [0 for i in range(10)]					# [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Set

Swift

var basket: Set = ["one", "two", "three"]let isExists = basket.contains("one")basket.insert("four")basket.update(with: "four") // if aleady contains will return `input`; else returns nil;// there is no inbuild method for appending listbasket.remove("four")basket.popFirst()basket.removeAll()

Python

basket = { "one", "two", "three"}
# or
basket = set({ "one", "two", "three"})isExists = "one" in basketbasket.add("four")basket.update(["five", "six"])basket.remove("six")basket.discard("six")   # If the item to remove does not exist, discard() will NOT raise an error.# take random element
random = basket.pop()   # threebasket.clear()   # set([])

Empty Set

Swift

var basket = Set<AnyHashable>()		// Set([])

Python

basket = set()						# set([])

Dictionaries

Swift

var info:[String: Any] = [
    "name": "Elit Vestibulum",
    "age": 43
]let name = info["name"]info["age"] = 54info["country"] = "Cursus Elit"
info.updateValue("Nibh Dapibus", forKey: "city")info.valuesinfo.keysinfo.removeValue(forKey: "age")info.removeAll()

Python

info = {
    "name" : "Elit Vestibulum",
    "age": 43
}# get 
name = info["name"]					
name = info.get("name")# update
info["age"] = 54# add new pairs
info["country"] = "Cursus Elit"
info.update({"city": "Nibh Dapibus"})	# get all values
values = info.values()   # get all keys
keys = info.keys()# remove pair
info.pop("age")info.clear()  # {}

Empty Dictionary

Swift

var info = [String: Any]()      // [:]

Python

info = dict()                  # {}

Class

Hello World

Swift

class MyClass {
    init() {
        print("Hello World")
    }
}let myObject = MyClass()

Python

class MyClass:
    def __init__(self):
        print("Hello World")
    
myObject = MyClass()

Basic Math Class Example

Swift

class Math {
    
    let pi = 3.14
    
    func areaOfCircle(radius r: Double) -> Double {
        return pi * (r * r)
    }
    
    func sum(a: Int, b: Int) -> Int {
        return a + b
    }
    
}let math = Math()
let area = math.areaOfCircle(radius: 10)
let sum = math.sum(a: 5, b: 2)

Python

class Math:
    pi = 3.14   # default initializer; to access `self` is required (ie. self.pi)
    
    def areaOfCircle(self, radius: float) -> float:
        return self.pi * (radius * radius)
        
    def sum(self, a, b):
        return a + b
        
    # Function annotations are completely optional metadata information about the types used by user-defined functions
    def substract(self, a: int, b: int) -> int:
        return a - b
    
math = Math()
area = math.areaOfCircle(10)			# 314.0
sum = math.sum(2, 5)				# 7
result = math.substract(2, 5)			# -3

Init Params

Swift

class Table {
    
    let multipler: Int
    
    init(input: Int) {
        self.multipler = input
    }
    
    func printTable(limit: Int = 10) {
        for i in 1 ... limit {
            print("\(multipler) * \(i) = \(i * multipler)")
        }
        print()
    }
}let table2 = Table(input: 2)
table2.printTable()
table2.printTable(limit: 5)

Python

class Table:
   def __init__(self, input):
      self.multipler = input
        
   def printTable(self, limit = 10):
      for i in range(1, limit):
         print("%d * %d = %d" % (self.multipler, i,  
                                 self.multipler * i))
         print()
        
        
table_2 = Table(2)
table_2.printTable()
table_2.printTable(5)output:
2 * 1 = 2 ..... 2 * 9 = 18
2 * 1 = 2 2 * 2 = 4 2 * 3 = 6 2 * 4 = 8

Class Inheritance, Overriding Methods

Swift

class Employee {
    let id: Int
    let name: String    init(id: Int, name: String) {
        self.id = id
        self.name = name
    }    func printDetails() {
        print("id: \(id)")
        print("name: \(name)")
    }
}class Technician: Employee {
    let labId: String
    init(id: Int, name: String, labId: String) {
        self.labId = labId
        super.init(id: id, name: name)
    }    override func printDetails() {
        super.printDetails()
        print("labId: \(labId)")
    }
}let technician = Technician(id: 2693, name: "Nibh Fringilla", labId: "LAB001")

Python

class Employee:
    def __init__(self, id, name):
        self.id = id
        self.name = name
        
    def printDetails(self):
        print("id: %s" % (self.id))
        print("name: %s" % (self.name))class Technician(Employee):
    def __init__(self, id, name, labID):
        self.labID = labID
        super().__init__(id, name)    # Override method
    def printDetails(self):
        super().printDetails()
        print("labID: %s" % (self.labID))
technician = Technician(2693, "Nibh Fringilla", "LAB001")
professor.printDetails()output:
id: 2693 name: Nibh Fringilla labID: LAB001

Private

Swift

class Hacker {
    
    private var name = "Amet Lorem"
    
    private func details() {
        print(name)
    }
    
    func publicDetails() {
        print("random name")
    }
}let hacker = Hacker()
hacker.publicDetails()      // random name

Python

class Hacker:
    __name = "Amet Lorem"    def __details(self):
        print(self.__name)
        
    def publicDetails(self):
        print("random name")
    
    
hacker = Hacker()
hacker.publicDetails()      # random name# "'Hacker' object has no attribute '..'" -- error for below commands
hacker.name
hacker.__name
hacker.details()
hacker.__details()

Structs, Data Classes

Swift

struct Center {
    let x: Float
    let y: Float
}// Equatable ~= __eq__
// Hashable ~= __hash__
// CustomStringConvertible ~= __repr__

Python

from dataclasses import dataclass@dataclass
class Center:
    x: float
    y: float
    
c1 = Center(4,5)
print(c1)            # Center(x=4, y=5)

Adventage of Data Classses: Auto generated _init_, _repr_, _eq_, ..

ref: https://medium.com/mindorks/understanding-python-dataclasses-part-1-c3ccd4355c34

@dataclass(frozen = True)	# immutable# To control the auto generated methods
@dataclass(init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False)

same functionality using class:

class Center:
    def __init__(self, x, y):
        self.x = x
        self.y = y    def __eq__(self, other):
        if (self.x == other.x and self.y == other.y):
            return True
        else:
            return False    def __repr__(self):
        return 'Point(x=%s, y=%s)' % (self.x, self.y)    # .. have to implement all functions manually

Closures

Basic

Swift

var addTen = { $0 + 10 }
addTen(5)     # 15

Python

lambda arguments: expression

Note: Only one expression (a + 10) is allowed with lambda functions.

addTen = lambda a: a + 10
addTen(5)       # 15# or use `def` if cannot achieve in single expressiondef addTen(a): 
    ..
    ..
    return a + 10

Multiple inputs

Swift

var product: ((Int, Int) -> (Int)) = { a, b in
    return a * b
}product(5, 10)

Python

product = lambda a, b: a * bproduct(5, 10)	# 50

Lambda function

Swift

func makeNTimes(_ n: Int) -> ((Int) -> Int) {
    return { a in return a * n }
}var doubler = makeNTimes(2)
doubler(10)
var tripler = makeNTimes(3)
tripler(10)

Python

def makeNTimes(n):
    return lambda a: a * n
    
doubler = makeNTimes(2)
doubler(10)	# 20tripler = makeNTimes(3)
tripler(10)	# 30

Map

Swift

let numbers = [1, 2, 3, 4, 5]let result = numbers.map { $0 * 2 }

Python

map(function, iterables)

numbers = [1, 2, 3, 4, 5]multiply2 = lambda x: x * 2result = list(map(multiply2, numbers))	# orresult = list(map(lambda x: x * 2, [1, 2, 3, 4, 5]))output:
[2, 4, 6, 8, 10]

Filter

Swift

let numbers = [1, 2, 3, 4, 5, 6]let result = numbers.filter { $0 % 2 == 0 }

Python

filter(function, iterable)

numbers = [1, 2, 3, 4, 5, 6]result = list(filter(lambda x : x % 2 == 0, numbers)) # [2, 4, 6]

Reduce

Swift

let numbers = [1, 2, 3, 4, 5, 6]let res = numbers.reduce(1) { (result, value) -> Int in
    return result * value
}

Python

reduce(function, iterable)

from functools import reducenumbers = [1, 2, 3, 4, 5, 6]exp = lambda x: x * 2product = reduce(exp, numbers)  
# 720

Exception Handling

User-defined Exceptions

Swift

enum InputValidationError: Error {
    case invalidInput(String)
}func validateAge(_ age: Int) throws {
    if age < 0 {
        throw InputValidationError.invalidInput("Only positive   integers are allowed")
    }
}
do {
    try validateAge(-2)
} catch InputValidationError.invalidInput(let message) {
    print("Exception: ", message)
}

Python

class InputValidationError(Exception):
   def __init__(self, message):
      self.message = messagedef validateAge(age):
    if age < 0:
        raise InputValidationError('Only positive integers are allowed')
try:
    validateAge(-1)
except InputValidationError as error:
    print("Exception: ", error.message)
except:
    print("something is wrong")

Example

Swift

enum CommonError: Error {
    case divisionByZero
}func divide(_ a: Int, by b: Int) throws -> Int {
    if b == 0 {
        throw CommonError.divisionByZero
    }
    return a / b
}
var result: Int
do {
    result = try divide(10, by: 0)
} catch CommonError.divisionByZero {
    print("division by zero!")
} catch {
    //
}Note: 
- In Swift there is no functionality to catch arbitrary runtime errors.
- no `finally` in swift, so make use of `defer`

Python

def divide(x, y):
     try:
         result = x / y
     except ZeroDivisionError:
         print("division by zero!")
     else:
         print("result is ", result)
     finally:
         print(".. executing finally")
>> divide(2, 1)
output:
result is 2.0
.. executing finally>> divide(2, 0)
division by zero!
.. executing finally

Unit Tests

Example

Swift

import XCTest
@testable import AppTargetclass AppHelperTests: XCTestCase {
    
    let calculator = Calculator()
    
    override func setUp() {
        super.setUp()
        // ..
    }
    
    override func tearDown() {
        // ..
        super.tearDown()
    }
    
    func testAdd() {
        let result = calculator.add(2, 3)
        XCTAssertEqual(result, 5)
    }
    
    func testMultiply() {
        let result = calculator.multiply(2, 3)
        XCTAssertEqual(result, 6)
    }
}

Python

calculator.py

def add(a, b):
    return a + b
    
def multiply(a, b):
    return a * b
import unittest
import calculatorclass TestCalculator(unittest.TestCase):    def setUp(self):
        pass
        
    def tearDown(self):
        pass
        
    def test_add(self):
        result = calculator.add(2, 3)
        self.assertEqual(result, 5)
        
    def test_multiply(self):
        result = calculator.multiply(2, 3)
        self.assertEqual(result, 6)

Running Tests

if __name__ == '__main__':
    unittest.main()
    
    
# Console output:
..
--------------------------------------------------------------------
Ran 2 tests in 0.000sOK

pass Statement:

used when a statement is required syntactically but you do not want any command or code to execute.

List of assets: ref: https://docs.python.org/2/library/unittest.html

Corrections are welcome :). Thank You.

Syntax Comparison: Swift vs Python

Import Modules

Constants

Variables

Comments

Print

Print Terminator Usage

Multiline Strings

String Interpolation

String Concatenation

How to get object type ?

String to Int

Binary to Number

Boolean

Tuples

Nil, None

del Statement

If Statement

If with Multiple Conditions

Escape characters

Counting Characters

Enum

Switch

Pass by reference

Decorators

Yield (instead of return), Next

Collection Types

Array

Array Operations

Empty array

Multidimensional arrays

Array Length

Array Slicing

Array with a Default Value

Set

Empty Set

Dictionaries

Empty Dictionary

Class

Hello World

Basic Math Class Example

Init Params

Class Inheritance, Overriding Methods

Private

Structs, Data Classes

Closures

Basic

Multiple inputs

Lambda function

Map

Filter

Reduce

Exception Handling

User-defined Exceptions

Example

Unit Tests

Example

Written by Kiran Sarella

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