Type conversion (int, float, string) in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does int() do in Python?

int() converts a value to an integer type. For example, it can turn a string like "123" or a float like 12.7 into an integer by removing the decimal part.

beginner

How do you convert a number to a string in Python?

You use the str() function. For example, str(10) becomes "10" as a string.

intermediate

What happens if you convert a string with decimals to int()?

It causes an error because int() expects a whole number string. You should convert it first to float() then to int() if needed.

beginner

What does float() do?

float() converts a value to a floating-point number (a number with decimals). For example, float("3.14") becomes 3.14.

beginner

Why is type conversion useful in programming?

Because sometimes you need to change data from one type to another to do calculations, display text, or store data correctly. For example, adding numbers needs numeric types, but showing them needs strings.

What will int("45") return?

A 45

B "45"

C 45.0

D Error

int("45") converts the string "45" to the integer 45.

What does str(3.14) return?

A "3.14"

B 3.14

C 3

D Error

str(3.14) converts the float 3.14 to the string "3.14".

Which function converts a number with decimals to an integer by removing decimals?

A str()

B int()

C float()

D bool()

int() converts a float to an integer by dropping the decimal part.

What happens if you try int("3.5") directly?

A Returns 3

B Returns 3.5

C Returns "3.5"

D Raises an error

int() cannot convert a string with decimals directly and raises a ValueError.

How to convert a string "7.8" to an integer 7?

A int("7.8")

B str(7.8)

C float("7.8") then int()

D int(str(7.8))

First convert the string to float, then convert that float to int: int(float("7.8")).

Explain how to convert between int, float, and string types in Python with examples.

Think about how to change numbers to text and text to numbers.

Describe a situation where type conversion is necessary in a program.

Imagine adding numbers entered as text.

Practice

1. What does the Python function int() do when applied to a string like '123'?

easy

A. Converts the string to the integer 123

B. Converts the string to the float 123.0

C. Leaves the string unchanged

D. Causes a syntax error

Solution

1. Step 1: Understand int() function behavior

   The int() function converts a string containing digits into an integer number.

2. Step 2: Apply int() to '123'

   Applying int('123') converts the string to the integer 123.

3. Final Answer:

   Converts the string to the integer 123 -> Option A

4. Quick Check:

   int('123') = 123 [OK]

Hint: int() turns digit strings into whole numbers [OK]

Common Mistakes:

• Thinking int() converts to float
• Expecting string unchanged
• Confusing with syntax error

2. Which of the following is the correct syntax to convert the float number 3.14 to an integer in Python?

easy

A. int(3,14)

B. int '3.14'

C. int(3.14)

D. int(3.14.0)

Solution

1. Step 1: Recall correct function call syntax

   Functions in Python require parentheses around arguments, e.g., int(3.14).

2. Step 2: Check each option

   int(3.14) uses correct syntax. Others have syntax errors or invalid argument formats.

3. Final Answer:

   int(3.14) -> Option C

4. Quick Check:

   int(3.14) is valid syntax [OK]

Hint: Use parentheses with int() for conversion [OK]

Common Mistakes:

• Omitting parentheses
• Using commas instead of dots
• Adding extra dots in numbers

3. What is the output of this code?

value = '45.67'
result = float(value)
print(int(result))

medium

A. 46

B. 45

C. Error

D. 45.67

Solution

1. Step 1: Convert string to float

   float('45.67') converts the string to the float number 45.67.

2. Step 2: Convert float to int

   int(45.67) converts the float to integer by dropping the decimal part, resulting in 45.

3. Final Answer:

   45 -> Option B

4. Quick Check:

   int(float('45.67')) = 45 [OK]

Hint: int() drops decimals, does not round [OK]

Common Mistakes:

• Expecting rounding to 46
• Printing float instead of int
• Confusing string and number types

4. The code below causes an error. What is the fix?

num = 'abc'
converted = int(num)
print(converted)

medium

A. Use float() instead of int()

B. Add quotes around int

C. Remove the int() conversion

D. Change 'abc' to a string of digits like '123'

Solution

1. Step 1: Identify cause of error

   Trying to convert 'abc' to int causes a ValueError because 'abc' is not numeric.

2. Step 2: Fix by using numeric string

   Replacing 'abc' with a string of digits like '123' allows int() to convert successfully.

3. Final Answer:

   Change 'abc' to a string of digits like '123' -> Option D

4. Quick Check:

   int('123') works, int('abc') errors [OK]

Hint: int() needs numeric strings, not letters [OK]

Common Mistakes:

• Using float() on non-numeric string
• Removing conversion but expecting int
• Adding quotes around function name

5. You have a list of mixed strings representing numbers: ['10', '20.5', '30', '40.0']. How do you convert all to integers correctly in Python?

hard

A. Use [int(float(x)) for x in list]

B. Use [int(x) for x in list]

C. Use [float(int(x)) for x in list]

D. Use [str(int(x)) for x in list]

Solution

1. Step 1: Understand list contents

   The list has strings representing integers and floats, e.g., '20.5' and '40.0'.

2. Step 2: Convert strings to float first

   Direct int() on '20.5' causes error, so convert to float first: float('20.5') = 20.5.

3. Step 3: Convert float to int

   Then convert float to int with int(20.5) = 20, dropping decimals.

4. Final Answer:

   Use [int(float(x)) for x in list] -> Option A

5. Quick Check:

   int(float('20.5')) = 20 [OK]

Hint: Convert string to float, then to int for decimals [OK]

Common Mistakes:

• Trying int() directly on float strings
• Swapping int and float conversions
• Converting to string instead of int