Learn Python in 10 Days: Day 3 - 拾光赋-拾光赋

Learn Python in 10 Days: Day 3

6个月前发布

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Today, we’re continuing our 10-day journey to learn Python, kicking off Day 3’s lesson. If you haven’t checked out Day 1 yet, you can find it here: Learn Python in 10 Days: Day 1

Hey there! Let’s dive into loops in Python, using some everyday examples and some hands-on coding. Here’s a breakdown of the main points, all formatted nicely for you.

Day 3: Loop Statements

Loops are everywhere in our daily lives, and just like that, they play a crucial role in programming as well. Let’s get down to the basics of loops in Python!

1. Basic Syntax of the `while` Loop

Basic `while` Loop in Python:


<span>i</span> <span>=</span> <span>0</span>
<span>while</span> <span>i</span> <span><</span> <span>100</span><span>:</span>
    <span>print</span><span>(</span><span>"</span><span>Hello, world!</span><span>"</span><span>)</span>
    <span>i</span> <span>+=</span> <span>1</span>
<span>i</span> <span>=</span> <span>0</span>
<span>while</span> <span>i</span> <span><</span> <span>100</span><span>:</span>
    <span>print</span><span>(</span><span>"</span><span>Hello, world!</span><span>"</span><span>)</span>
    <span>i</span> <span>+=</span> <span>1</span>
i = 0
while i < 100:
    print("Hello, world!")
    i += 1

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Explanation:
1. The while loop continues as long as the condition is True.
2. You need to set a condition to stop the loop, like i += 1 paired with i < 100 to avoid an infinite loop.
3. Indentation is crucial, just like with if statements.

Example: Sum of Numbers from 1 to 100


<span>i</span> <span>=</span> <span>1</span>
<span>total</span> <span>=</span> <span>0</span>
<span>while</span> <span>i</span> <span><=</span> <span>100</span><span>:</span>
    <span>total</span> <span>+=</span> <span>i</span>
    <span>i</span> <span>+=</span> <span>1</span>
<span>print</span><span>(</span><span>f</span><span>"</span><span>The total sum is: </span><span>{</span><span>total</span><span>}</span><span>"</span><span>)</span>
<span>i</span> <span>=</span> <span>1</span>
<span>total</span> <span>=</span> <span>0</span>
<span>while</span> <span>i</span> <span><=</span> <span>100</span><span>:</span>
    <span>total</span> <span>+=</span> <span>i</span>
    <span>i</span> <span>+=</span> <span>1</span>
<span>print</span><span>(</span><span>f</span><span>"</span><span>The total sum is: </span><span>{</span><span>total</span><span>}</span><span>"</span><span>)</span>
i = 1
total = 0
while i <= 100:
    total += i
    i += 1
print(f"The total sum is: {total}")

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Example: Guess the Number Game


<span>import</span> <span>random</span>
<span>num</span> <span>=</span> <span>random</span><span>.</span><span>randint</span><span>(</span><span>1</span><span>,</span> <span>100</span><span>)</span>
<span>count</span> <span>=</span> <span>0</span>
<span>flag</span> <span>=</span> <span>True</span>
<span>while</span> <span>flag</span><span>:</span>
    <span>guess_num</span> <span>=</span> <span>int</span><span>(</span><span>input</span><span>(</span><span>"</span><span>Guess the number: </span><span>"</span><span>))</span>
    <span>count</span> <span>+=</span> <span>1</span>
    <span>if</span> <span>guess_num</span> <span>==</span> <span>num</span><span>:</span>
        <span>print</span><span>(</span><span>"</span><span>Congratulations! You guessed it!</span><span>"</span><span>)</span>
        <span>flag</span> <span>=</span> <span>False</span>
    <span>elif</span> <span>guess_num</span> <span>></span> <span>num</span><span>:</span>
        <span>print</span><span>(</span><span>"</span><span>Too high!</span><span>"</span><span>)</span>
    <span>else</span><span>:</span>
        <span>print</span><span>(</span><span>"</span><span>Too low!</span><span>"</span><span>)</span>
<span>print</span><span>(</span><span>f</span><span>"</span><span>You guessed it in </span><span>{</span><span>count</span><span>}</span><span> tries.</span><span>"</span><span>)</span>
<span>import</span> <span>random</span>

<span>num</span> <span>=</span> <span>random</span><span>.</span><span>randint</span><span>(</span><span>1</span><span>,</span> <span>100</span><span>)</span>
<span>count</span> <span>=</span> <span>0</span>
<span>flag</span> <span>=</span> <span>True</span>

<span>while</span> <span>flag</span><span>:</span>
    <span>guess_num</span> <span>=</span> <span>int</span><span>(</span><span>input</span><span>(</span><span>"</span><span>Guess the number: </span><span>"</span><span>))</span>
    <span>count</span> <span>+=</span> <span>1</span>
    <span>if</span> <span>guess_num</span> <span>==</span> <span>num</span><span>:</span>
        <span>print</span><span>(</span><span>"</span><span>Congratulations! You guessed it!</span><span>"</span><span>)</span>
        <span>flag</span> <span>=</span> <span>False</span>
    <span>elif</span> <span>guess_num</span> <span>></span> <span>num</span><span>:</span>
        <span>print</span><span>(</span><span>"</span><span>Too high!</span><span>"</span><span>)</span>
    <span>else</span><span>:</span>
        <span>print</span><span>(</span><span>"</span><span>Too low!</span><span>"</span><span>)</span>

<span>print</span><span>(</span><span>f</span><span>"</span><span>You guessed it in </span><span>{</span><span>count</span><span>}</span><span> tries.</span><span>"</span><span>)</span>
import random

num = random.randint(1, 100)
count = 0
flag = True

while flag:
    guess_num = int(input("Guess the number: "))
    count += 1
    if guess_num == num:
        print("Congratulations! You guessed it!")
        flag = False
    elif guess_num > num:
        print("Too high!")
    else:
        print("Too low!")

print(f"You guessed it in {count} tries.")

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2. Nested `while` Loops

Example: Sum of Factorials from 1 to 100


<span>i</span> <span>=</span> <span>1</span>
<span>total_sum</span> <span>=</span> <span>0</span>
<span>while</span> <span>i</span> <span><=</span> <span>100</span><span>:</span>
    <span>fact</span> <span>=</span> <span>1</span>
    <span>j</span> <span>=</span> <span>1</span>
    <span>while</span> <span>j</span> <span><=</span> <span>i</span><span>:</span>
        <span>fact</span> <span>*=</span> <span>j</span>
        <span>j</span> <span>+=</span> <span>1</span>
    <span>total_sum</span> <span>+=</span> <span>fact</span>
    <span>i</span> <span>+=</span> <span>1</span>
<span>print</span><span>(</span><span>total_sum</span><span>)</span>
<span>i</span> <span>=</span> <span>1</span>
<span>total_sum</span> <span>=</span> <span>0</span>

<span>while</span> <span>i</span> <span><=</span> <span>100</span><span>:</span>
    <span>fact</span> <span>=</span> <span>1</span>
    <span>j</span> <span>=</span> <span>1</span>
    <span>while</span> <span>j</span> <span><=</span> <span>i</span><span>:</span>
        <span>fact</span> <span>*=</span> <span>j</span>
        <span>j</span> <span>+=</span> <span>1</span>
    <span>total_sum</span> <span>+=</span> <span>fact</span>
    <span>i</span> <span>+=</span> <span>1</span>

<span>print</span><span>(</span><span>total_sum</span><span>)</span>
i = 1
total_sum = 0

while i <= 100:
    fact = 1
    j = 1
    while j <= i:
        fact *= j
        j += 1
    total_sum += fact
    i += 1

print(total_sum)

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Example: Multiplication Table (9×9)


<span>i</span> <span>=</span> <span>1</span>
<span>while</span> <span>i</span> <span><=</span> <span>9</span><span>:</span>
    <span>j</span> <span>=</span> <span>1</span>
    <span>while</span> <span>j</span> <span><=</span> <span>i</span><span>:</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>{</span><span>i</span><span>}</span><span>*</span><span>{</span><span>j</span><span>}</span><span>=</span><span>{</span><span>i</span><span>*</span><span>j</span><span>}</span><span>\t</span><span>"</span><span>,</span> <span>end</span><span>=</span><span>''</span><span>)</span>
        <span>j</span> <span>+=</span> <span>1</span>
    <span>i</span> <span>+=</span> <span>1</span>
    <span>print</span><span>()</span>  <span># New line after each row </span>
<span>i</span> <span>=</span> <span>1</span>
<span>while</span> <span>i</span> <span><=</span> <span>9</span><span>:</span>
    <span>j</span> <span>=</span> <span>1</span>
    <span>while</span> <span>j</span> <span><=</span> <span>i</span><span>:</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>{</span><span>i</span><span>}</span><span>*</span><span>{</span><span>j</span><span>}</span><span>=</span><span>{</span><span>i</span><span>*</span><span>j</span><span>}</span><span>\t</span><span>"</span><span>,</span> <span>end</span><span>=</span><span>''</span><span>)</span>
        <span>j</span> <span>+=</span> <span>1</span>
    <span>i</span> <span>+=</span> <span>1</span>
    <span>print</span><span>()</span>  <span># New line after each row </span>
i = 1
while i <= 9:
    j = 1
    while j <= i:
        print(f"{i}*{j}={i*j}\t", end='')
        j += 1
    i += 1
    print()  # New line after each row

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3. Basic Syntax of the `for` Loop

Unlike while, for loops are used for iterating over a sequence (like a list, tuple, dictionary, set, or string).

Example: Iterating Over a String


<span>name</span> <span>=</span> <span>"</span><span>Bob</span><span>"</span>
<span>for</span> <span>char</span> <span>in</span> <span>name</span><span>:</span>
    <span>print</span><span>(</span><span>char</span><span>,</span> <span>end</span><span>=</span><span>''</span><span>)</span>
<span>name</span> <span>=</span> <span>"</span><span>Bob</span><span>"</span>
<span>for</span> <span>char</span> <span>in</span> <span>name</span><span>:</span>
    <span>print</span><span>(</span><span>char</span><span>,</span> <span>end</span><span>=</span><span>''</span><span>)</span>
name = "Bob"
for char in name:
    print(char, end='')

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Example: Counting Occurrences of ‘a’ in a String


<span>sample_str</span> <span>=</span> <span>"</span><span>abcdefaac</span><span>"</span>
<span>count</span> <span>=</span> <span>0</span>
<span>for</span> <span>char</span> <span>in</span> <span>sample_str</span><span>:</span>
    <span>if</span> <span>char</span> <span>==</span> <span>'</span><span>a</span><span>'</span><span>:</span>
        <span>count</span> <span>+=</span> <span>1</span>
<span>print</span><span>(</span><span>count</span><span>)</span>
<span>sample_str</span> <span>=</span> <span>"</span><span>abcdefaac</span><span>"</span>
<span>count</span> <span>=</span> <span>0</span>
<span>for</span> <span>char</span> <span>in</span> <span>sample_str</span><span>:</span>
    <span>if</span> <span>char</span> <span>==</span> <span>'</span><span>a</span><span>'</span><span>:</span>
        <span>count</span> <span>+=</span> <span>1</span>
<span>print</span><span>(</span><span>count</span><span>)</span>
sample_str = "abcdefaac"
count = 0
for char in sample_str:
    if char == 'a':
        count += 1
print(count)

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`range()` Function:

Syntax 1: range(num) generates numbers from 0 to num-1.
Syntax 2: range(start, end) generates numbers from start to end-1.
Syntax 3: range(start, end, step) uses a step value.

Example: Counting Even Numbers


<span>num</span> <span>=</span> <span>int</span><span>(</span><span>input</span><span>(</span><span>"</span><span>Enter a number: </span><span>"</span><span>))</span>
<span>count</span> <span>=</span> <span>0</span>
<span>for</span> <span>x</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>num</span><span>):</span>
    <span>if</span> <span>x</span> <span>%</span> <span>2</span> <span>==</span> <span>0</span><span>:</span>
        <span>count</span> <span>+=</span> <span>1</span>
<span>print</span><span>(</span><span>count</span><span>)</span>
<span>num</span> <span>=</span> <span>int</span><span>(</span><span>input</span><span>(</span><span>"</span><span>Enter a number: </span><span>"</span><span>))</span>
<span>count</span> <span>=</span> <span>0</span>

<span>for</span> <span>x</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>num</span><span>):</span>
    <span>if</span> <span>x</span> <span>%</span> <span>2</span> <span>==</span> <span>0</span><span>:</span>
        <span>count</span> <span>+=</span> <span>1</span>

<span>print</span><span>(</span><span>count</span><span>)</span>
num = int(input("Enter a number: "))
count = 0

for x in range(1, num):
    if x % 2 == 0:
        count += 1

print(count)

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4. Nested `for` Loops

Example: Multiplication Table (9×9) with `for` Loops


<span>for</span> <span>i</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>10</span><span>):</span>
    <span>for</span> <span>j</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>i</span><span>+</span><span>1</span><span>):</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>{</span><span>i</span><span>}</span><span>*</span><span>{</span><span>j</span><span>}</span><span>=</span><span>{</span><span>i</span><span>*</span><span>j</span><span>}</span><span>\t</span><span>"</span><span>,</span> <span>end</span><span>=</span><span>''</span><span>)</span>
    <span>print</span><span>()</span>  <span># New line after each row </span>
<span>for</span> <span>i</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>10</span><span>):</span>
    <span>for</span> <span>j</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>i</span><span>+</span><span>1</span><span>):</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>{</span><span>i</span><span>}</span><span>*</span><span>{</span><span>j</span><span>}</span><span>=</span><span>{</span><span>i</span><span>*</span><span>j</span><span>}</span><span>\t</span><span>"</span><span>,</span> <span>end</span><span>=</span><span>''</span><span>)</span>
    <span>print</span><span>()</span>  <span># New line after each row </span>
for i in range(1, 10):
    for j in range(1, i+1):
        print(f"{i}*{j}={i*j}\t", end='')
    print()  # New line after each row

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5. Loop Control Statements: `break` and `continue`

continue: Skips the rest of the code inside the loop for the current iteration only.
break: Terminates the loop.

Example: Payroll with Performance Check


<span>money</span> <span>=</span> <span>10000</span>
<span>for</span> <span>num</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>21</span><span>):</span>
    <span>grade</span> <span>=</span> <span>random</span><span>.</span><span>randint</span><span>(</span><span>1</span><span>,</span> <span>10</span><span>)</span>
    <span>if</span> <span>grade</span> <span><</span> <span>5</span><span>:</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>Employee </span><span>{</span><span>num</span><span>}</span><span> has a performance score below 5. No salary issued.</span><span>"</span><span>)</span>
        <span>continue</span>
    <span>if</span> <span>money</span> <span>>=</span> <span>1000</span><span>:</span>
        <span>money</span> <span>-=</span> <span>1000</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>Employee </span><span>{</span><span>num</span><span>}</span><span> meets performance criteria. Company balance: </span><span>{</span><span>money</span><span>}</span><span>"</span><span>)</span>
    <span>else</span><span>:</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>Insufficient funds. Balance: </span><span>{</span><span>money</span><span>}</span><span>"</span><span>)</span>
        <span>break</span>
<span>money</span> <span>=</span> <span>10000</span>

<span>for</span> <span>num</span> <span>in</span> <span>range</span><span>(</span><span>1</span><span>,</span> <span>21</span><span>):</span>
    <span>grade</span> <span>=</span> <span>random</span><span>.</span><span>randint</span><span>(</span><span>1</span><span>,</span> <span>10</span><span>)</span>
    <span>if</span> <span>grade</span> <span><</span> <span>5</span><span>:</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>Employee </span><span>{</span><span>num</span><span>}</span><span> has a performance score below 5. No salary issued.</span><span>"</span><span>)</span>
        <span>continue</span>

    <span>if</span> <span>money</span> <span>>=</span> <span>1000</span><span>:</span>
        <span>money</span> <span>-=</span> <span>1000</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>Employee </span><span>{</span><span>num</span><span>}</span><span> meets performance criteria. Company balance: </span><span>{</span><span>money</span><span>}</span><span>"</span><span>)</span>
    <span>else</span><span>:</span>
        <span>print</span><span>(</span><span>f</span><span>"</span><span>Insufficient funds. Balance: </span><span>{</span><span>money</span><span>}</span><span>"</span><span>)</span>
        <span>break</span>
money = 10000

for num in range(1, 21):
    grade = random.randint(1, 10)
    if grade < 5:
        print(f"Employee {num} has a performance score below 5. No salary issued.")
        continue

    if money >= 1000:
        money -= 1000
        print(f"Employee {num} meets performance criteria. Company balance: {money}")
    else:
        print(f"Insufficient funds. Balance: {money}")
        break

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原文链接：Learn Python in 10 Days: Day 3

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