Code Comments
Both languages have comments:# Python has single line comments // Swift has single line comments /* Swift also has multi-line comments in C style */
Declaring Constants and Variables
Swift has rich support for type inference and constants. Python is dynamic and does not natively support constants.name = "A string variable in Python" age = 42 # An integer variable in Python var name = "A string variable in Swift" var age : Int // An explicit integer variable in Swift age = 42 let pi = 3.14 // Constant in Swift
Integer Bounds
# Python does not have upper bounds for integer numbers (Python 3) large_nun = 10000000000000000000000000000000000000000000000000000 // Swift var a = Int32.min var b = Int32.max
Type Inference
Swift is a strongly-typed language which makes heavy use of type-inference although you can declare explicit types. Python is a dynamic language so while there is a type system it is not evident in the syntax.# Python name = "Michael" # string variable, but can change name = 42 # would run n = 42 # currently an int d = 42.0 # currently a float // Swift var name = "Michael" // string name = 42 // Error var n = 42 // int var d = 42.0 // double
String Comparison
Python and Swift both have Unicode strings. Python generally has richer string support than Swift (especially around string formatting).# python
a = "some text"
b = "some text"
if a == b:
print("The strings are equal")
# swift
var a = "some text"
var b = "some text"
if a == b {
println("The strings are equal")
}
Both languages have many functions on strings# python
if a.startswith("some"):
print("Starts with some")
if a.endswith("some"):
print("Ends with some")
// swift
if a.hasPrefix("some") {
println("Starts with some")
}
if a.hasSuffix("some") {
println("Endss with some")
}
String Upper or Lower Case
# python s = "some text" u = s.upper() l = s.lower() // swift var s = "some text" var u = s.uppercaseString var l = s.lowercaseString
Declaring Arrays
Neither language has strict array types in the sense of C-based arrays. The arrays in Swift and Python are closer to lists. Python’s lists are not typed (hence can be heterogeneous).# python nums = [1,1,3,5,8,13,21] // swift var nums = [1,1,3,5,8,13,21] // int array var strings = ["one", "two", "three"] // string array
Working with Arrays
# Iteration in python
nums = [1,1,3,5,8,13,21]
for n in nums:
print(n)
# Iteration in Swift:
var nums = [1,1,3,5,8,13,21]
for n in nums {
println(n)
}
# Element access
n = nums[2] # python, n = 3
var n = nums[2] # swift, n = 3
# Updating values
nums[2] = 10 # python
nums[2] = 10 # swift
# Check for elements
# python
if nums:
print("Nums is not empty")
// swift
if !nums.isEmpty {
println("Nums is not empty")
}
# Adding items:
nums.append(7) # python
nums.append(7) # swift
# Slicing
nums = [1,1,3,5,8,13,21]
middle = nums[2:4] # python, middle = [3, 5]
var middle = nums[2..<4] // swift, middle = [3,5]
Dictionaries
Dictionaries play important roles in both languages and are fundamental types.# python
d = dict(name="Michael", state="OR")
d = { "name": "Michael", "state": "OR" }
the_name = d["name"]
// swift
var empty_dict = Dictionary<String, String>()
var d = ["name": "Michael", "state": "OR"]
var the_name = d["name"]
Adding items is the same in both languages. Removing entries is arguably clearer in Swift.
# add an item
d["hobby"] = "Biking" # python
d["hobby"] = "Biking" // swift
# remove an item
del d["hobby"] # python
d.removeValueForKey("hobby") // swift
Checking for the existence of a key can also be done in both languages.
# python
if "hobby" in d:
print("Your hobby is " + d["hobby"])
// swift
if let theHobby = d["hobby"] {
println("Your hobby is \(theHobby)")
}
Conditional Statements
Conditional statements are quite similar.# python
n = 40
m = 2
if n > 40:
print("n bigger than 40")
elif m == 2 and n % 2 == 0:
print("m is 2")
else:
print("else")
# swift
var n = 40
var m = 2
if n > 40 {
println("n bigger than 40")
}
else if m == 2 && n % 2 == 0 {
print("m is 2")
}
else {
print("else")
}
Switch statements
Swift has them, Python does not.Functions
Functions are very rich in both languages. They have closures, multiple return values, lambdas, and more. Here is a simple version. Note that this example also leverages tuples and tuple unpacking in both languages.
# python
def get_user(id):
name = "username"
email = "email"
return name,email
n, e = get_user(1)
// swift
func getUser(id : Int) -> (String, String) {
var username = "username"
var email = "email"
return (username, email)
}
var (n, e) = getUser(1) // n = username, e = email
