Expression and statement in python

In Python, what is the difference between expressions and statements?

Chris Martin

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asked Jan 18, 2011 at 19:19

1

Expressions only contain identifiers, literals and operators, where operators include arithmetic and boolean operators, the function call operator [] the subscription operator [] and similar, and can be reduced to some kind of "value", which can be any Python object. Examples:

3 + 5
map[lambda x: x*x, range[10]]
[a.x for a in some_iterable]
yield 7

Statements [see 1, 2], on the other hand, are everything that can make up a line [or several lines] of Python code. Note that expressions are statements as well. Examples:

# all the above expressions
print 42
if x: do_y[]
return
a = 7

songololo

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answered Jan 18, 2011 at 19:27

Sven MarnachSven Marnach

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15

Expression -- from the New Oxford American Dictionary:

expression: Mathematics a collection of symbols that jointly express a quantity : the expression for the circumference of a circle is 2πr.

In gross general terms: Expressions produce at least one value.

In Python, expressions are covered extensively in the Python Language Reference In general, expressions in Python are composed of a syntactically legal combination of Atoms, Primaries and Operators.

Python expressions from Wikipedia

Examples of expressions:

Literals and syntactically correct combinations with Operators and built-in functions or the call of a user-written functions:

>>> 23
23
>>> 23l
23L
>>> range[4]
[0, 1, 2, 3] 
>>> 2L*bin[2]
'0b100b10'
>>> def func[a]:      # Statement, just part of the example...
...    return a*a     # Statement...
... 
>>> func[3]*4
36    
>>> func[5] is func[a=5]
True

Statement from Wikipedia:

In computer programming a statement can be thought of as the smallest standalone element of an imperative programming language. A program is formed by a sequence of one or more statements. A statement will have internal components [e.g., expressions].

Python statements from Wikipedia

In gross general terms: Statements Do Something and are often composed of expressions [or other statements]

The Python Language Reference covers Simple Statements and Compound Statements extensively.

The distinction of "Statements do something" and "expressions produce a value" distinction can become blurry however:

• List Comprehensions are considered "Expressions" but they have looping constructs and therfore also Do Something.
• The if is usually a statement, such as if x a+ b, 0];

  Function calls, arithmetic and boolean operations are good examples of expressions.

  Expressions are often part of a statement.

  The distinction between the two is often required to indicate whether we require a pice of code to return a value.

  answered Aug 8, 2020 at 9:15

  Alex SAlex S

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  STATEMENT:

  A Statement is a action or a command that does something. Ex: If-Else,Loops..etc

  val a: Int = 5
  If[a>5] print["Hey!"] else print["Hi!"]
  

  EXPRESSION:

  A Expression is a combination of values, operators and literals which yields something.

  val a: Int = 5 + 5 #yields 10
  

  answered Mar 9, 2019 at 15:33

  Raja ShekarRaja Shekar

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  2

  References

  Expressions and statements

  2.3 Expressions and statements - thinkpython2 by Allen B. Downey

  2.10. Statements and Expressions - How to Think like a Computer Scientist by Paul Resnick and Brad Miller

  An expression is a combination of values, variables, and operators. A value all by itself is considered an expression, and so is a variable, so the following are all legal expressions:

  >>> 42
  42
  >>> n
  17
  >>> n + 25
  42
  
  

  When you type an expression at the prompt, the interpreter evaluates it, which means that it finds the value of the expression. In this example, n has the value 17 and n + 25 has the value 42.

  A statement is a unit of code that has an effect, like creating a variable or displaying a value.

  >>> n = 17
  >>> print[n]
  

  The first line is an assignment statement that gives a value to n. The second line is a print statement that displays the value of n. When you type a statement, the interpreter executes it, which means that it does whatever the statement says. In general, statements don’t have values.

  answered Aug 25, 2020 at 8:51

  blessedblessed

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  An expression translates to a value.

  A statement consumes a value* to produce a result**.

  *That includes an empty value, like: print[] or pop[].

  **This result can be any action that changes something; e.g. changes the memory [ x = 1] or changes something on the screen [ print["x"] ].

  A few notes:

  • Since a statement can return a result, it can be part of an expression.
  • An expression can be part of another expression.

  answered Nov 18, 2020 at 10:18

  PontiosPontios

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  Statements before could change the state of our Python program: create or update variables, define function, etc.

  And expressions just return some value can't change the global state or local state in a function.

  But now we got :=, it's an alien!

  answered Dec 28, 2019 at 15:24

  roachsinairoachsinai

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  Expressions:

  • Expressions are formed by combining objects and operators.
  • An expression has a value, which has a type.
  • Syntax for a simple expression:

  2.0 + 3 is an expression which evaluates to 5.0 and has a type float associated with it.

  Statements

  Statements are composed of expression[s]. It can span multiple lines.

  answered Aug 22, 2017 at 23:33

  ObiWanObiWan

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  A statement contains a keyword.

  An expression does not contain a keyword.

  print "hello" is statement, because print is a keyword.

  "hello" is an expression, but list compression is against this.

  The following is an expression statement, and it is true without list comprehension:

  [x*2 for x in range[10]]
  

  Racil Hilan

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  answered Mar 31, 2014 at 13:29

  2

  Think of statements as consecutive actions or instructions that your program executes. So, value assignments, if clauses, together with for and while loops, are all statements. Function and class definitions are statements, too.

  Think of expressions as anything that can be put into an if clause. Typical examples of expressions are literals, values returned by operators [excluding in-place operators], and comprehensions, such as list, dictionary, and set comprehensions. Function calls and method calls are expressions, too.

  Python 3.8 introduced the dedicated := operator, which assigns a value to the variable but acts as an expression instead of a statement. Due to its visual appearance, it was quickly nicknamed the walrus operator.

  answered May 20 at 8:52

  Python calls expressions "expression statements", so the question is perhaps not fully formed.

  A statement consists of pretty much anything you can do in Python: calculating a value, assigning a value, deleting a variable, printing a value, returning from a function, raising an exception, etc. The full list is here: //docs.python.org/reference/simple_stmts.html#

  An expression statement is limited to calling functions [e.g., math.cos[theta]"], operators [ e.g., "2+3"], etc. to produce a value.

  answered Jan 18, 2011 at 19:29

  Walter NissenWalter Nissen

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