Notice: This page requires JavaScript to function properly.
Please enable JavaScript in your browser settings or update your browser.Learn Type Conversion Essentials | Cross-Type Interactions
Data Types in Python

bookType Conversion Essentials

Type conversion lets you move between core Python types so values can be compared, calculated, or displayed.

Converting to int

int(x) makes an integer.

  • From an int: returns the same number;
  • From a float: truncates toward zero (for example, int(2.9) returns 2, int(-2.9) returns -2);
  • From a string: the string must represent an integer (optional spaces and sign are ok).

Valid Conversions


              
12345678910

            
# Converting different types of user input to integers
age_input = "  42  "
temperature_reading = 2.9
negative_balance = -2.9

print(int(age_input))            # 42 β†’ clean string converted to int
print(int(temperature_reading))  # 2  β†’ fractional part truncated
print(int(negative_balance))     # -2 β†’ also truncates toward zero
print(int("7"))                  # 7  β†’ string number becomes integer
print(int("   -15  "))           # -15 β†’ handles spaces and sign
copy

These Raise ValueError


              
12

            
int("2.5")        # ValueError - not an integer string
int("42a")        # ValueError
copy

Converting to float

float(x) makes a floating-point number.

  • Works for ints and decimal or scientific-notation strings;
  • Commas are not decimal points in Python.

Valid conversions


              
12345678

            
# Converting numeric inputs for a shopping calculator
quantity = 3
price_str = "2.5"
discount_factor = "1e3"  # scientific notation for 1000

print(float(quantity))        # 3.0 β†’ integer converted to float
print(float(price_str))       # 2.5 β†’ string price converted to float
print(float(discount_factor)) # 1000.0 β†’ converts from scientific notation
copy

These Raise ValueError


              
1

            
float("2,5")   # ValueError - use a dot, not a comma
copy

Converting to str

str(x) makes a human-readable string representation. Prefer f-strings when you are building messages.


              
12345678910

            
# Formatting a student's exam result
student_age = 42
average_score = 3.5

print(str(student_age))       # "42" β†’ number converted to string
print(str(average_score))     # "3.5" β†’ float converted to string

student_name, final_score = "Ada", 98
report_message = f"{student_name} scored {final_score} points on the exam."
print(report_message)
copy

Converting to bool

bool(x) follows Python truthiness rules.

  • Numbers: 0 is False, any other number is True;
  • Strings: "" (empty) is False, any non-empty string is True (even "0" and "False").

              
123456789101112

            
# Checking how different user inputs behave as boolean values
login_attempts = 0
notifications = 7
username = ""
user_id = "0"
status = "False"

print(bool(login_attempts))  # False β†’ 0 means no attempts yet
print(bool(notifications))   # True  β†’ non-zero means new notifications
print(bool(username))        # False β†’ empty string means no username entered
print(bool(user_id))         # True  β†’ any non-empty string is truthy
print(bool(status))          # True  β†’ text "False" is still a non-empty string
copy

Mistakes to Avoid

  • int("2.5") raises ValueError - parse as float() first, then truncate or round;
  • Locale habit: "2,5" is invalid - use "2.5";
  • Underscores in input strings: "1_000" is invalid - remove underscores first: "1_000".replace("_", "");
  • Truthiness surprise: bool("0") is True - compare string contents explicitly if needed, for example s == "0".

1. What does each line produce?

2. Which call raises a ValueError?

3. Pick the correct statement.

question-icon

What does each line produce?

int(3.9) β†’
int(" -8 ")
bool("0")

Click or drag`n`drop items and fill in the blanks

question mark

Which call raises a ValueError?

Select the correct answer

question mark

Pick the correct statement.

Select the correct answer

Everything was clear?

How can we improve it?

Thanks for your feedback!

SectionΒ 4. ChapterΒ 1

Ask AI

expand

Ask AI

ChatGPT

Ask anything or try one of the suggested questions to begin our chat

Suggested prompts:

Can you explain more about how type conversion works in Python?

What happens if I try to convert a string that isn't a valid number?

Can you show examples of converting between other types, like lists or dictionaries?

Awesome!

Completion rate improved to 3.45

bookType Conversion Essentials

Swipe to show menu

Type conversion lets you move between core Python types so values can be compared, calculated, or displayed.

Converting to int

int(x) makes an integer.

  • From an int: returns the same number;
  • From a float: truncates toward zero (for example, int(2.9) returns 2, int(-2.9) returns -2);
  • From a string: the string must represent an integer (optional spaces and sign are ok).

Valid Conversions


              
12345678910

            
# Converting different types of user input to integers
age_input = "  42  "
temperature_reading = 2.9
negative_balance = -2.9

print(int(age_input))            # 42 β†’ clean string converted to int
print(int(temperature_reading))  # 2  β†’ fractional part truncated
print(int(negative_balance))     # -2 β†’ also truncates toward zero
print(int("7"))                  # 7  β†’ string number becomes integer
print(int("   -15  "))           # -15 β†’ handles spaces and sign
copy

These Raise ValueError


              
12

            
int("2.5")        # ValueError - not an integer string
int("42a")        # ValueError
copy

Converting to float

float(x) makes a floating-point number.

  • Works for ints and decimal or scientific-notation strings;
  • Commas are not decimal points in Python.

Valid conversions


              
12345678

            
# Converting numeric inputs for a shopping calculator
quantity = 3
price_str = "2.5"
discount_factor = "1e3"  # scientific notation for 1000

print(float(quantity))        # 3.0 β†’ integer converted to float
print(float(price_str))       # 2.5 β†’ string price converted to float
print(float(discount_factor)) # 1000.0 β†’ converts from scientific notation
copy

These Raise ValueError


              
1

            
float("2,5")   # ValueError - use a dot, not a comma
copy

Converting to str

str(x) makes a human-readable string representation. Prefer f-strings when you are building messages.


              
12345678910

            
# Formatting a student's exam result
student_age = 42
average_score = 3.5

print(str(student_age))       # "42" β†’ number converted to string
print(str(average_score))     # "3.5" β†’ float converted to string

student_name, final_score = "Ada", 98
report_message = f"{student_name} scored {final_score} points on the exam."
print(report_message)
copy

Converting to bool

bool(x) follows Python truthiness rules.

  • Numbers: 0 is False, any other number is True;
  • Strings: "" (empty) is False, any non-empty string is True (even "0" and "False").

              
123456789101112

            
# Checking how different user inputs behave as boolean values
login_attempts = 0
notifications = 7
username = ""
user_id = "0"
status = "False"

print(bool(login_attempts))  # False β†’ 0 means no attempts yet
print(bool(notifications))   # True  β†’ non-zero means new notifications
print(bool(username))        # False β†’ empty string means no username entered
print(bool(user_id))         # True  β†’ any non-empty string is truthy
print(bool(status))          # True  β†’ text "False" is still a non-empty string
copy

Mistakes to Avoid

  • int("2.5") raises ValueError - parse as float() first, then truncate or round;
  • Locale habit: "2,5" is invalid - use "2.5";
  • Underscores in input strings: "1_000" is invalid - remove underscores first: "1_000".replace("_", "");
  • Truthiness surprise: bool("0") is True - compare string contents explicitly if needed, for example s == "0".

1. What does each line produce?

2. Which call raises a ValueError?

3. Pick the correct statement.

question-icon

What does each line produce?

int(3.9) β†’
int(" -8 ")
bool("0")

Click or drag`n`drop items and fill in the blanks

question mark

Which call raises a ValueError?

Select the correct answer

question mark

Pick the correct statement.

Select the correct answer

Everything was clear?

How can we improve it?

Thanks for your feedback!

SectionΒ 4. ChapterΒ 1
some-alt