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Python makes decisions by evaluating a condition as true or false, then running the matching if, elif, or else block. Operators let you build those conditions: comparisons test values, in checks membership, and and, or, and not combine or reverse conditions.
The examples below use standard Python 3 syntax documented in the Python 3.14.7 tutorial and language reference. The core operators and branching behavior described here are longstanding Python features.
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Start with a comparison and an if
A comparison produces a Boolean result: True or False. An if statement runs its indented block when its condition is true.
temperature = 22
if temperature > 20:
print("It's warm")The colon ends the condition, and indentation marks which statements belong to the block. In Python, indentation is part of the program’s structure, not just visual formatting. See the Python tutorial on control flow.
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Add else and ordered elif branches
Use else for a fallback when the preceding if condition is false. Add one or more elif clauses when there are additional conditions to test. Python checks them in order and runs the first branch whose condition is true; it skips the rest.
score = 82
if score >= 90:
grade = "A"
elif score >= 80:
grade = "B"
else:
grade = "Keep practicing"Here, a score of 82 fails the first test and reaches the second. The final else handles scores that meet neither threshold. Branch order matters when conditions overlap: a condition that matches early prevents later branches from being considered. elif is short for “else if” and keeps alternatives from requiring nested if blocks.
Choose the operator that matches the question
Python has distinct operators for comparing values, checking membership, and testing whether two references point to the same object. The Python tutorial’s conditions section and the language reference on comparisons describe these behaviors.
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| Question | Operator | Example |
|---|---|---|
| Are these values equal or different? | ==, != |
answer == "yes" |
| Is one value less than, at most, greater than, or at least another? | <, <=, >, >= |
age >= 18 |
| Does a collection contain a value? | in, not in |
answer in ("y", "yes") |
| Are two references to the same object? | is, is not |
value is None |
== checks value equality; is checks object identity. Two separately created objects may have equal values without being the same object. Use == for ordinary value comparisons and use identity tests when identity itself matters, commonly to check for None.
Do not confuse = with ==: = assigns a value, while == asks whether two values are equal.
Use chained comparisons for ranges
A chained comparison expresses a range clearly. For example, 0 <= score < 100 is equivalent to 0 <= score and score < 100, except that the middle expression is evaluated only once.
if 0 <= score < 100:
print("Score is in range")Chaining compares adjacent values: a < b > c means a < b and b > c; it does not compare a directly with c.
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Combine conditions with and, or, and not
Use and when both conditions must hold, or when either can hold, and not to negate a condition. Parentheses make intended grouping easier to see, especially when combining different operators.
if (age >= 18) and has_id:
print("Entry allowed")
if answer == "y" or answer == "yes":
print("Continuing")
if not is_paused:
print("Running")Python evaluates arithmetic before comparisons, comparisons before not, then and, then or. Thus not a == b means not (a == b). When a condition mixes and and or, add parentheses rather than making a reader reconstruct precedence. The language reference on expressions lists the precedence rules.
Short-circuiting and the value returned
and stops once it finds a false operand; or stops once it finds a true operand. Any later operand is not evaluated. This short-circuit behavior can guard an operation, but avoid hiding side effects in complex conditions.
In addition, and and or return one of their operands, not necessarily a Boolean:
name = "Ada"
shown_name = name or "Guest" # "Ada"
empty_name = ""
shown_empty_name = empty_name or "Guest" # "Guest"Here, or returns the first truthy operand, or the final operand if none is truthy. and returns the first false operand, or the final operand if all are truthy. In an if condition, Python tests the resulting value’s truthiness.
Conditions can use truthiness, not just comparisons
A condition does not have to contain a comparison. Python treats False, None, numeric zero, and empty strings and containers as false; most other values are true. Objects can customize this behavior with a __bool__() method. These rules are covered in the Python language reference.
items = []
if items:
print("There are items")
else:
print("The list is empty")An empty list is false in a condition, while a non-empty list is true. This concise check is useful when the question is simply whether a collection contains anything. If you need to distinguish an empty collection from other false values, test the specific condition you mean.
Use a conditional expression for a simple value choice
A conditional expression selects and returns one of two values:
status = "adult" if age >= 18 else "minor"Its form is value_if_true if condition else value_if_false. It is an expression, so it fits a short assignment or other simple value choice. Use statement-based if/elif/else when the branches perform multiple actions or the choice would be hard to read on one line.
When to use if or match
Use if/elif/else for ranges, compound conditions, and branches that depend on arbitrary true-or-false tests. Python’s match statement can be useful when selecting among patterns, such as constant-like values or the structure of an object, but it is not a universal replacement for if. The control-flow tutorial discusses both tools.
Quick Recap
- Choose
ifwhen conditions express comparisons or logic. - Choose
matchwhen the decision is naturally expressed as matching a value or pattern. - Use a conditional expression only when choosing one value is simpler than writing branches.
Common mistakes to avoid
- Using
=instead of==: assignment and equality testing are different operations. - Using
isfor ordinary value comparisons: use==to compare values; reserveisfor identity checks such asvalue is None. - Assuming
andandoralways produceTrueorFalse: they return an operand according to short-circuit evaluation. - Relying on unclear precedence: use parentheses to show how compound conditions are grouped.
- Forgetting that
elifis ordered: an earlier true branch prevents later alternatives from running.
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