Numeric validation (gt, lt, ge, le) in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to require the query parameter 'age' to be greater than 18.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items/")
async def read_items(age: int = Query(..., gt=[1])):
    return {"age": age}

Drag options to blanks, or click blank then click option'

A18

B0

C21

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using ge instead of gt changes the condition to 'greater or equal'.

Setting the value to less than 18 allows younger ages.

The gt parameter in Query sets the minimum value that the query parameter must be greater than. Here, it is set to 18.

2fill in blank

medium

Complete the code to require the query parameter 'price' to be less than 100.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/products/")
async def get_products(price: float = Query(..., lt=[1])):
    return {"price": price}

Drag options to blanks, or click blank then click option'

A50

B100

C150

D200

Attempts:

3 left

💡 Hint

Common Mistakes

Using le instead of lt allows price equal to 100.

Setting the value higher than 100 does not restrict prices below 100.

The lt parameter means 'less than'. Setting lt=100 means the price must be below 100.

3fill in blank

hard

Fix the error in the code to require 'quantity' to be greater or equal to 1.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/orders/")
async def get_orders(quantity: int = Query(..., [1]=1)):
    return {"quantity": quantity}

Drag options to blanks, or click blank then click option'

Ale

Bgt

Cge

Dlt

Attempts:

3 left

💡 Hint

Common Mistakes

Using gt excludes 1 from valid values.

Using le or lt sets upper limits instead.

The ge parameter means 'greater or equal'. Setting ge=1 allows quantity 1 or more.

4fill in blank

hard

Fill both blanks to require 'rating' to be between 1 and 5 inclusive.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/reviews/")
async def get_reviews(rating: int = Query(..., [1]=1, [2]=5)):
    return {"rating": rating}

Drag options to blanks, or click blank then click option'

Age

Bgt

Cle

Dlt

Attempts:

3 left

💡 Hint

Common Mistakes

Using gt or lt excludes boundary values.

Swapping the order of parameters causes errors.

Use ge=1 for minimum value 1 and le=5 for maximum value 5, both inclusive.

5fill in blank

hard

Fill all three blanks to require 'score' to be greater than 0, less than or equal to 100, and default to 50.

FastAPI

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/scores/")
async def get_scores(score: int = Query([1], gt=[2], [3]=100)):
    return {"score": score}

Drag options to blanks, or click blank then click option'

A50

B0

Cle

Dlt

Attempts:

3 left

💡 Hint

Common Mistakes

Using lt instead of le excludes 100.

Setting default value outside the valid range causes errors.

The default value is set to 50. The score must be greater than 0 (gt=0) and less than or equal to 100 (le=100).

Practice

1. In FastAPI, which parameter would you use in a Pydantic Field to ensure a number is strictly greater than 10?

easy

A. gt=10

B. lt=10

C. ge=10

D. le=10

Solution

1. Step 1: Understand the meaning of gt

   The gt parameter means "greater than" and excludes the value itself.

2. Step 2: Match the requirement

   Since the question asks for strictly greater than 10, gt=10 is the correct choice.

3. Final Answer:

   gt=10 -> Option A

4. Quick Check:

   Strictly greater than 10 = gt=10 [OK]

Hint: Use gt for strictly greater than, ge for greater or equal [OK]

Common Mistakes:

• Confusing gt with ge and using ge=10 instead
• Using lt or le which mean less than
• Thinking gt includes the number 10

2. Which of the following is the correct syntax to validate a number field in FastAPI to be less than or equal to 100 using Pydantic?

easy

A. Field(ge=100)

B. Field(lt=100)

C. Field(le=100)

D. Field(gt=100)

Solution

1. Step 1: Identify the parameter for less than or equal

   The parameter le stands for "less than or equal to".

2. Step 2: Check the syntax

   The correct syntax is Field(le=100) to enforce the value to be at most 100.

3. Final Answer:

   Field(le=100) -> Option C

4. Quick Check:

   Less than or equal to 100 = le=100 [OK]

Hint: Use le for less or equal, lt for strictly less [OK]

Common Mistakes:

• Using lt=100 which excludes 100
• Using ge or gt which are for greater values
• Writing Field(le100) without equals sign

3. Given this FastAPI model snippet:

from pydantic import BaseModel, Field

class Item(BaseModel):
    price: float = Field(gt=0, le=100)

What happens if you send a request with price=0?

medium

A. Accepted because price is a float

B. Accepted because price is less than or equal to 100

C. Validation error because price must be less than or equal to 0

D. Validation error because price must be greater than 0

Solution

1. Step 1: Analyze the validation rules

   The field has gt=0 (greater than 0) and le=100 (less or equal to 100).

2. Step 2: Check the input value

   Input price is 0, which is not greater than 0, so it violates the gt=0 rule.

3. Final Answer:

   Validation error because price must be greater than 0 -> Option D

4. Quick Check:

   Price 0 fails gt=0 validation [OK]

Hint: gt excludes the number itself; 0 is not > 0 [OK]

Common Mistakes:

• Thinking 0 passes because it is less than 100
• Confusing gt with ge and allowing 0
• Ignoring validation errors in FastAPI

4. You wrote this FastAPI model:

from pydantic import BaseModel, Field

class User(BaseModel):
    age: int = Field(ge=18, lt=65)

But when you send age=65, it passes validation. Why?

medium

A. Because lt=65 means less than 65, so 65 should fail but it passes because you used le=65 instead of lt=65

B. Because lt=65 means less than 65, so 65 should fail but it passes because you used ge incorrectly

C. Because lt=65 means less than 65, so 65 should fail but it passes because the validation is not enforced on int

D. Because lt=65 means age must be less than 65, so 65 should fail but it passes due to a bug

Solution

1. Step 1: Understand the meaning of lt and le

   lt=65 means strictly less than 65, so 65 should fail validation.

2. Step 2: Identify the cause of passing validation

   If 65 passes, likely the code uses le=65 (less or equal) instead of lt=65, allowing 65.

3. Final Answer:

   Because lt=65 means less than 65, so 65 should fail but it passes because you used le=65 instead of lt=65 -> Option A

4. Quick Check:

   lt excludes value; le includes it [OK]

Hint: lt excludes value; le includes it. Check which you used [OK]

Common Mistakes:

• Confusing lt and le parameters
• Assuming validation is not enforced on integers
• Thinking ge affects upper bound

5. You want to create a FastAPI model for a product rating that must be between 1 and 5 inclusive. Which is the correct way to define this field using Pydantic validation?

hard

A. rating: int = Field(gt=1, lt=5)

B. rating: int = Field(ge=1, le=5)

C. rating: int = Field(gt=1, le=5)

D. rating: int = Field(ge=1, lt=5)

Solution

1. Step 1: Understand inclusive range requirements

   Inclusive means the value can be equal to the limits, so use ge (greater or equal) and le (less or equal).

2. Step 2: Match parameters to the range 1 to 5 inclusive

   Use ge=1 and le=5 to allow 1 and 5 as valid values.

3. Final Answer:

   rating: int = Field(ge=1, le=5) -> Option B

4. Quick Check:

   Inclusive range uses ge and le [OK]

Hint: Use ge and le for inclusive ranges, gt and lt for exclusive [OK]

Common Mistakes:

• Using gt or lt excludes boundary values
• Mixing gt with le or ge with lt incorrectly
• Forgetting to include both bounds