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
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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