Type checking with `type()`, type conversion `int()`, `float()`, `str()`

1.2.5 · Coding › Introduction to Programming (Python)

1. Label padhna: `type()`

Worked example Types padhna

type(7)        # <class 'int'>
type(7.0)      # <class 'float'>
type("7")      # <class 'str'>
type(7 == 7)   # <class 'bool'>

Yeh step kyun? Dekho ki 7, 7.0, aur "7" ek insaan ko milte-julte lagte hain lekin Python teeno ko alag types manta hai — aur unhe bilkul alag treat karta hai.

2. Label badalna: conversion functions

Yeh constructor functions hain: yeh original ko modify nahi karte, yeh nai value build karte hain.

HAR EK KAISA BEHAVE KARTA HAI (woh rules jo tumhe kaatenge)

Figure — Type checking with `type()`, type conversion `int()`, `float()`, `str()`

3. Worked examples

Worked example (a)

"3" + "4" ko theek karna

a = "3"
b = "4"
print(a + b)              # "34"  ← string join
print(int(a) + int(b))    # 7     ← numeric add

Yeh step kyun? int() text "3" ko number 3 ke roop mein re-label karta hai, toh + ab addition matlab hai.

Worked example (b) User input padhna (hamesha ek string hoti hai!)

age = input("Age? ")      # input() HAMESHA str return karta hai
print(type(age))          # <class 'str'>
age = int(age)            # convert karo taaki math kar sakein
print(age + 1)            # agla birthday

Yeh step kyun? input() tumhe text deta hai chahe user ne digits type ki hon. int() ke bina, age + 1 crash ho jaata (str + int illegal hai).

Worked example (d) Truncation vs rounding

int(2.99)     # 2  (kaata gaya, 3 pe round NAHI hua)
round(2.99)   # 3  (rounding ke liye round() use karo)
int(-2.99)    # -2 (toward zero)

Yeh step kyun? Steel-manning: lagta hai jaise int() nearest par round karna chahiye. Nahi karta — yeh fractional part delete kar deta hai. Rounding ke liye round() yaad rakho.

4. Common mistakes (Steel-man + fix)

5. Active recall

Recall Khud test karne ke liye click karo

type("7") kya print karta hai? → <class 'str'>
int(-3.7) kya hai? → -3 (toward zero)
input() hamesha kya return karta hai? → ek str
"3"+"4" kyun "34" deta hai? → strings par + = join, add nahi
"3.9" ko safely int mein kaise convert karein? → int(float("3.9"))
type() vs isinstance() — code mein decide karne ke liye kaun sa? → isinstance()

Recall Feynman: ek 12-saal ke bachchey ko explain karo

Imagine karo ki cheezón ke har box par ek sticker hai: "WHOLE NUMBERS", "DECIMALS", ya "WORDS". type() woh hai jab tum sticker oonchi awaaz mein padhte ho. Sticker padhne se box ke andar kya hai woh nahi badalta. int(), float(), str() jaise hain copy karna — contents ko ek naye box mein naye sticker ke saath — kabhi kabhi kuch kho jaata hai (decimals chop ho jaate hain jab "WHOLE NUMBERS" box mein copy karte hain), aur kabhi kabhi copy refuse kar deta hai (tum "apple" word ko numbers box mein nahi daal sakte). Original box untouched rehta hai.

6. Connections

Variables and Assignment — conversions usually x = int(x) ke saath paired hote hain
Input and Output (input, print) — input() str return karta hai, toh conversion zaroori hai
Operators and Expressions — + ka matlab type par depend karta hai
Booleans and Truthiness — bool ek subclass hai int ka
Errors and Exceptions — ValueError / TypeError buri conversions se
Floating Point Representation — kyun float approximate hota hai

type(x) kya return karta hai?

x ka class/type object, jaise <class 'int'>; yeh sirf padhta hai, kabhi x nahi badalta.

type(7.0) ka result aur type?

<class 'float'>.

int(3.9) kya deta hai aur kyun?

3 — int() truncates toward zero (fractional part kaatta hai), yeh round NAHI karta.

int(-3.9) kya deta hai?

-3 (truncation toward zero hota hai, negative infinity ki taraf nahi).

int("3.9") kyun fail karta hai?

string par int() ko ek clean integer string chahiye; dot ise ValueError banata hai. int(float("3.9")) use karo.

"3" + "4" kya evaluate hota hai?

"34" — strings par + concatenate (join) karta hai, add nahi karta.

Strings "3" aur "4" ko numerically kaise add karte hain?

int("3") + int("4") → 7.

input() hamesha kaun sa type return karta hai?

Ek str, chahe user ne digits type ki hon.

"score: " + str(95) mein str(95) kyun use karte hain?

Tum str + int concatenate nahi kar sakte; str() number ko pehle text mein convert karta hai.

int(True) aur int(False)?

Respectively 1 aur 0 (bool int ka subclass hai).

type() vs isinstance() — kaun sa kab use karna hai?

type() exact type inspect/print karne ke liye; isinstance(x, T) code mein decide karne ke liye (subclasses bhi match karta hai).

Kya int(x) x ko modify karta hai?

Nahi — yeh ek nai value return karta hai; tumhe x = int(x) se reassign karna hoga.