Filtering with Conditions (and, or, isin, query)

Setup

A boolean filter works in two steps: first you build a mask — a Series of True/False, one per row — then you use that mask to keep only the True rows.

Setup DataFrame

import pandas as pd
 
df = pd.DataFrame({
    "name": ["Asha", "Ravi", "Meera", "Zoya", "Kabir"],
    "age": [23, 28, 26, 31, 22],
    "city": ["Pune", "Delhi", "Delhi", "Pune", "Mumbai"],
    "score": [88, 91, 77, 95, 60],
})
 
print(df)

Basic boolean filtering

Single condition

print(df[df["age"] >= 25])

Multiple conditions: AND / OR

Pandas uses bitwise operators:

• AND: &
• OR: |

Always use parentheses:

AND filter

mask = (df["city"] == "Delhi") & (df["score"] >= 80)
print(df[mask])

OR filter

mask = (df["city"] == "Mumbai") | (df["score"] >= 90)
print(df[mask])

isin() for membership checks

isin

mask = df["city"].isin(["Pune", "Delhi"])
print(df[mask])

between() for range filters

between

mask = df["age"].between(23, 30, inclusive="both")
print(df[mask])

query() for readable filters

query() can be easier to read, especially in notebooks.

query

result = df.query('city == "Delhi" and score >= 80')
print(result)

Variables inside query

query with variable

min_score = 85
result = df.query('score >= @min_score')
print(result)

Common mistakes

• Using and / or instead of & / | (will error)
• Forgetting parentheses around conditions
• Comparing strings with extra spaces (clean using .str.strip())

Common pitfall

df[(df["a"] > 1) & (df["b"] < 5)] needs the parentheses around each condition — Python’s & binds tighter than >/<, so df["a"] > 1 & df["b"] < 5 silently does the wrong thing instead of raising an error. Always parenthesize each side of &/|.

Visualize it

diagram Boolean mask filtering mermaid

  flowchart LR
  A["df['score'] >= 80"] --> B["Boolean mask (True/False per row)"]
  B --> C["df[mask]"]
  C --> D["Only matching rows"]

A condition produces a True/False mask; indexing with that mask keeps only the True rows.

sketch A condition becomes a keep/drop mask p5.js Pause Restart

Each row is tested against the condition; only rows where the mask is True survive the filter.

🧪 Try It Yourself

Exercise 1 – Build a Boolean Mask

pch.exerciseTag pch.exerciseTitle

Exercise 2 – Combine Conditions With &

pch.exerciseTag pch.exerciseTitle

Exercise 3 – Membership With isin

pch.exerciseTag pch.exerciseTitle

Next

Once you can pull out the rows you want, the next skill is reordering them — continue to Sorting and Ranking.