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Datatyper i Python

bookGrundlæggende Typekonvertering

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


              
123456

            
age_input = " 42 "
print(int(age_input))      # 42
print(int(2.9))            # 2
print(int(-2.9))           # -2
print(int("7"))            # 7
print(int(" -15 "))        # -15
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


              
123

            
print(float(3))            # 3.0
print(float("2.5"))        # 2.5
print(float("1e3"))        # 1000.0
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.


              
123

            
print(str(42))             # "42"
print(str(3.5))            # "3.5"
print(f"Ada scored {98} points.")
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").

              
12345

            
print(bool(0))             # False
print(bool(7))             # True
print(bool(""))            # False
print(bool("0"))           # True
print(bool("False"))       # True
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. Which call raises a ValueError?

2. Pick the correct statement.

question mark

Which call raises a ValueError?

Select the correct answer

question mark

Pick the correct statement.

Select the correct answer

Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 4. Kapitel 1

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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


              
123456

            
age_input = " 42 "
print(int(age_input))      # 42
print(int(2.9))            # 2
print(int(-2.9))           # -2
print(int("7"))            # 7
print(int(" -15 "))        # -15
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


              
123

            
print(float(3))            # 3.0
print(float("2.5"))        # 2.5
print(float("1e3"))        # 1000.0
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.


              
123

            
print(str(42))             # "42"
print(str(3.5))            # "3.5"
print(f"Ada scored {98} points.")
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").

              
12345

            
print(bool(0))             # False
print(bool(7))             # True
print(bool(""))            # False
print(bool("0"))           # True
print(bool("False"))       # True
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. Which call raises a ValueError?

2. Pick the correct statement.

question mark

Which call raises a ValueError?

Select the correct answer

question mark

Pick the correct statement.

Select the correct answer

Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 4. Kapitel 1
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