Python syntax

In this article we will look at the main differences in Python syntax compared to other languages. In this section, by other languages we mainly mean C like languages (C/C++, Java etc), as these are the most commonly used languages.

Comments

Python uses the # character to mark the rest of the line as a comment (similar to // in other languages). It doesn't use support block comments (there is no equivalent to /* ... */).

Statements

• Python does not require a semicolon at the end of a statement
• Every statement must be on a separate line

x = a + b
print(x)

Variables

• Variables are untyped - any variable can hold any type of data
• Variables do not need to be declared, you create a variable by assigning a value to it

x = 3         # x holds an integer
y = 7.8       # y holds a float
x = 'abc'     # Now x holds a string

Code blocks

• Like other languages, Python uses nested blocks for if statements, loops and function bodies
• A block is introduced by a colon
• All statements in a block must be indented by the same amount
• The end of a block is indicated by the indentation returning to its previous level

if a > b:      # Colon starts block
      a = b      # This line is part of the if block
      b = 0      # This line is also part of the if block
print(a)       # This line is not part of the if block

If statements

• Python uses if and else like many other languages
• You can use elif for extra clauses
• It is not necessary to put brackets around conditions, and most programmers don't
• Python has no switch statement - use if statements with elif clauses instead

if a == 1
    # Case 1
elif a == 2
    # Case 2
else
    # Other cases

Conditions

• Python uses comparison operators such as > or != similar to many other languages
• Compound conditions use keywords and, or, not (rather than &&, ||, !)
• A numerical value of 0 tests as false, any other value is true. Similarly a list or string tests as false if empty, true if not empty

While loops

• Similar to other languages, but with Python block syntax
• There is no do ... while construct

a = 5
while a > 0:
      print(a)
      a -= 1

For loops

• for loops always loop over a sequence, such as a list or the characters of a string
• The range function creates a sequence of numbers, similar to a tradition C style for loop

for i in range(5):   # equivalent to for(i = 0; i < 5; i++)
      print(i)

Defining functions

• Functions are defined using def keyword
• Parameters can be given default values
• There are many more options, see declaring functions

def add(a, b, c=0):       # c is optional, defaults to 0
      return a + b + c

Calling functions

• Similar to other languages
• Parameters with default values can be omitted
• You can use parameter names, either for clarity or to reorder them
• There are many more options, see calling functions

 add(1, 2)             # c defaults to 0
 add(2, 4, 6)          # c is now 6
 add (a=2, b=4, c=6)   # Naming the parameters

If you found this article useful, you might be interested in the book Functional Programming in Python, or other books, by the same author.

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