1. The "Law of Interchange" of the four basic data types in Python
The core data types of Python include:int(integer)、float (float)、str(String)、bool (boolean value). Here are the tips for converting them:
String → integer/floating point number
# string to integerage = "25"
print(int(age)) # Output: 25
# string to floating point numberprice = "99.9"
print(float(price)) # Output: 99.9
# ⚠️ Big pit warning! Non-numeric strings will report an errortry:
age = "twenty-five"
print(int(age)) # Report an error: ValueError: invalid literal for int() with base 10: 'twenty-five'except ValueError as e:
print(f"ValueError: {e}")
Skill:usetry-exceptCatch exceptions to avoid program crashes!
Integer/Float Number → String
# Number to string (must be required for splicing and log output)num = 100
print(str(num) + "%") # Output: 100%
# Floating point numbers retain two decimal placespi = 3.1415926
print(f"{pi:.2f}") # Output: 3.14 (recommended f-string formatting)"Hidden Rules" for Boolean Values
# Other types → Boolean value (0, empty value will be converted to False!)print(bool(0)) # False
print(bool("")) # False
print(bool([])) # False
print(bool("Hi")) # True
# Boolean value → integer (True=1, False=0)print(int(True)) # 1
print(float(False))# 0.0
"Automatic upgrade" of integers and floating-point numbers
# When integer and floating point operations, the result will be automatically upgraded to floatresult = 5 + 3.14 print(result) # 8.14 (type float) # Explicit conversion priorityprint(float(10)) # 10.0 print(int(8.88)) # 8 (Direct truncation, non-rounding!)
2. A guide to avoid pits that spread across the Internet!
Pit 1：input()The input default is a string, and it must be converted before mathematical calculation!
user_input = input("Please enter the number:") # Enter "123"result = int(user_input) * 2
print(result) # 246
Pit 2：int()When converting floating point numbers, discard the decimals directly, useround()Rounding is more reliable!
print(int(9.99)) # 9 print(round(9.99)) # 10
Pit 3：bool("False")It turned out to be True! Because non-empty strings are True!
print(bool("False")) # True (String is not empty)print(bool(0)) # False
3. Advanced skills: eval() function and implicit conversion
# eval() can parse string expressions, but use them with caution (safety risk)expression = "3 + 4 * 2"
print(eval(expression)) # 11
# Implicit conversion: Automatic bool conversion in if conditiondata = []
if data:
print("There is data")
else:
print("Empty list!") # Output: empty list!4. Master all conversion relationships in one form
| method | illustrate |
|---|---|
| int(x [,base ]) | Convert x to an integer |
| float(x ) | Convert x to a floating point number |
| complex(real [,imag ]) | Create a plural |
| str(x ) | Convert object x to string |
| repr(x ) | Convert object x to expression string |
| eval(str ) | Used to calculate valid Python expressions in a string and return an object |
| tuple(s ) | Convert sequence s to a tuple |
| list(s ) | Convert sequence s to a list |
| chr(x ) | Convert an integer to a character |
| unichr(x ) | Convert an integer to Unicode characters |
| ord(x ) | Convert a character to its integer value |
| hex(x ) | Convert an integer to a hexadecimal string |
| oct(x ) | Convert an integer to an octal string |
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