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Types de Données en Python

bookPrincipes Fondamentaux de la Conversion de Types

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


              
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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
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These Raise ValueError


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


              
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print(float(3))            # 3.0
print(float("2.5"))        # 2.5
print(float("1e3"))        # 1000.0
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These Raise ValueError


              
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float("2,5")   # ValueError - use a dot, not a comma
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Converting to str

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


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

              
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print(bool(0))             # False
print(bool(7))             # True
print(bool(""))            # False
print(bool("0"))           # True
print(bool("False"))       # True
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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

Tout était clair ?

Comment pouvons-nous l'améliorer ?

Merci pour vos commentaires !

Section 4. Chapitre 1

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bookPrincipes Fondamentaux de la Conversion de Types

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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

Tout était clair ?

Comment pouvons-nous l'améliorer ?

Merci pour vos commentaires !

Section 4. Chapitre 1
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