The key to writing Python's if else statements is to understand the logical structure and details. 1. The infrastructure is to execute a piece of code if conditions are established, otherwise the else part is executed, else is optional; 2. Multi-condition judgment is implemented using elif, and it is executed sequentially and stopped once it is met; 3. Nested if is used for further subdivision judgment, it is recommended not exceeding two layers; 4. In simple scenarios, ternary expressions can be used instead of simple if else. Only by paying attention to indentation, conditional order and logical integrity can we write clear and stable judgment codes.
It is actually not difficult to write if else statements in Python. The key is how to use them clearly and practically. When novices first start learning, they often tend to confuse the order or indentation format of conditional judgment, resulting in the program not being able to produce the expected results. This article uses several common examples to talk about how to use if else correctly and some small details that need to be paid attention to.
Infrastructure: if and else
The simplest if else structure is to determine whether a condition is true. If it is true, execute the code in the if, otherwise execute the else part. for example:
age = 16
if age >= 18:
print("You are already an adult")
else:
print("You are underage")This structure is suitable for scenarios where there are only two situations that need to be handled. Note that else is optional . Sometimes you only need to do something when the condition is met. If it is not met, don't care about it.
Multi-condition judgment: the role of elif
When you want to judge multiple different situations, you need to use elif (equivalent to else if). For example, judging grades:
score = 75
if score >= 90:
print("A")
elif score >= 80:
print("B")
elif score >= 70:
print("C")
else:
print("D")A few points to note:
- The conditions are judged from top to bottom. Once a certain item is established, you will not read the subsequent ones.
- Else is executed only when all conditions are not met.
- The order is very important . For example, put
score >= 70in the first judgment, and the subsequent ones may not be executed.
Nested if: judge again in judgment
Sometimes you need to further subdivided judgment based on the results of a certain judgment. At this time, you can use nested if:
age = 20
has_license = True
if age >= 18:
if has_license:
print("You can drive legally")
else:
print("You need to take the driver's license")
else:
print("You can't drive yet")Don’t have too deep nesting levels, usually two layers are enough. If it is too complicated, it is recommended to split the logic or encapsulate it with functions.
Concise writing: ternary expressions replace simple if else
For judgments that only one or two lines of operations, you can use ternary expressions to simplify the code:
x = 10 result = "big" if x > 5 else "small" print(result)
This writing method is suitable for simple assignment or return value operations and is not recommended to make complex logical judgments.
Basically that's it. If else looks simple, but using it well does not just write the grammar right. The key is to clear logic and comprehensive coverage of conditions. Practice a few more examples and you can slowly write a more stable judgment structure.
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