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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Python’s str.find() method returns the lowest (first) index where a substring occurs, or -1 when it is absent. Its syntax is string.find(sub[, start[, end]]). For example, "Python makes text processing easy".find("text") returns 19. Indexes are zero-based, and searching does not modify the original immutable string.
The official documentation recommends find() when you need the position; use the in operator when you only need a yes/no answer (Python documentation).
What find() does
find() searches a string for a literal substring and reports where the first complete match begins.
text = "Hello, Python!"
position = text.find("Python")
print(position) # 7It returns one index, not every match. Python strings are immutable, so the method only reads the string.
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Syntax and search bounds
str.find(sub[, start[, end]])sub: the substring to locate.start: optional inclusive starting index.end: optional exclusive ending index.
The optional bounds follow slice-style interpretation, equivalent in meaning to searching within text[start:end] without writing that slice explicitly.
text = "Python is widely used"
print(text.find("is")) # 7
print(text.find("is", 8)) # -1
print(text.find("is", 0, 10)) # 7Because end is exclusive, the complete match must fit before that boundary:
text = "abcdef"
print(text.find("cd", 0, 4)) # 2
print(text.find("cd", 0, 3)) # -1Negative bounds use the same rules as slicing. They can be useful, but explicit nonnegative bounds are often clearer in beginner and maintenance code.
text = "Python programming"
print(text.find("Python", -10)) # 0
print(text.find("Python", 0, -1)) # 0
print(text.find("x", 100)) # -1Basic results and the -1 sentinel
When a match exists
text = "apple banana apple"
print(text.find("apple")) # 0The result is the lowest matching index.
When no match exists
position = "Python".find("Java")
print(position) # -1-1 is a normal return value, not an exception. Check it explicitly:
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position = text.find("Java")
if position == -1:
print("Substring not found")
else:
print(f"Found at index {position}")The index-zero truthiness trap
Do not use the result directly as a Boolean. Index 0 is falsey:
text = "Python"
if text.find("Python"):
print("Found") # does not runUse position != -1, or use in when the index is unnecessary.
find() versus in
| Need | Preferred expression |
|---|---|
| First position | text.find("Python") |
| Existence only | "Python" in text |
if "Python" in text:
print("The text contains Python")For strings, membership is defined as a substring test; the language reference notes the equivalent test text.find(sub) != -1 (membership-test documentation). Choose in for clearer intent when no location is needed.
find() versus index()
text = "Python"
print(text.find("Java")) # -1
print(text.index("Java")) # raises ValueErrorindex() has the same search parameters but raises ValueError if absent (index() documentation). Use it when missing text means invalid input or an exceptional state:
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try:
position = text.index("required")
except ValueError:
print("Required substring is missing")Finding later, last, and multiple matches
Second and subsequent non-overlapping matches
text = "apple banana apple"
needle = "apple"
first = text.find(needle)
second = text.find(needle, first + len(needle))
print(first, second) # 0 13Using len(needle) avoids a hard-coded offset.
All matches
def find_all(text, needle):
if needle == "":
raise ValueError("needle must not be empty")
positions = []
start = 0
while True:
position = text.find(needle, start)
if position == -1:
return positions
positions.append(position)
start = position + len(needle)
print(find_all("red blue red green red", "red")) # [0, 9, 19]Advancing by len(needle) skips overlapping matches. Advance by one character when overlaps should count:
text = "aaaa"
needle = "aa"
positions = []
start = 0
while True:
position = text.find(needle, start)
if position == -1:
break
positions.append(position)
start = position + 1
print(positions) # [0, 1, 2]Rightmost match with rfind()
rfind() returns the highest matching index (documentation).
path = "archive/2026/report.pdf"
dot = path.rfind(".")
if dot != -1:
extension = path[dot + 1:]For actual filesystem paths, prefer pathlib:
from pathlib import Path
extension = Path("report.final.csv").suffixCase-insensitive and Unicode-aware searching
find() is case-sensitive:
"Python".find("Python") # 0
"Python".find("python") # -1For simple ASCII data, normalize both values with lower(). For broader Unicode case handling, casefold() is generally preferable:
text = "Python Programming"
needle = "python"
position = text.casefold().find(needle.casefold())
print(position) # 0Case folding can change character relationships in some languages. If the returned index must refer precisely to the original string, test the target language data rather than assuming the normalized index maps directly. Unicode normalization may also matter: visually identical strings such as precomposed é and eu0301 can have different underlying representations.
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Empty needles
An empty string is considered a substring. Its result is the beginning of the permitted range:
text = "Python"
print(text.find("")) # 0
print(text.find("", 3)) # 3
print(text.find("", 3, 5)) # 3Validate user-supplied search terms when an empty query is not meaningful:
needle = user_input.strip()
if not needle:
print("Please enter a non-empty search term")Literal text, words, and regular expressions
find() searches character sequences, not whole words and not patterns:
"concatenate".find("cat") # 3
"cat".find("at") # 1
"Order 123".find(r"d+") # -1; searches literal backslash, d, and +Use re.search() for character classes, alternatives, quantifiers, groups, or boundary rules:
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import re
match = re.search(r"d+", "Order 123")
if match:
print(match.start()) # 6Do not introduce a regular expression when a literal search expresses the requirement more clearly.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Strings, bytes, and compatible types
str.find() returns a string index, not a UTF-8 byte offset:
text = "café"
print(text.find("é"))For encoded data, search bytes consistently:
data = "café".encode("utf-8")
print(data.find("é".encode("utf-8")))Mixing text and bytes raises TypeError:
"abc".find(b"b") # TypeErrorDecode bytes before text processing, or keep both haystack and needle as bytes. Avoid blindly converting arbitrary values with str(); explicit type validation prevents hidden data-quality errors. Python documents separate methods for text and binary sequences (bytes and bytearray operations).
Practical patterns and better alternatives
Extracting text after a known marker
line = "Name: Ada Lovelace"
marker = "Name: "
position = line.find(marker)
if position != -1:
name = line[position + len(marker):]For a required prefix, a dedicated operation is clearer:
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if line.startswith("Name: "):
name = line.removeprefix("Name: ")Detecting a delimiter
header = "Content-Type: text/plain"
colon = header.find(":")
if colon != -1:
key = header[:colon]
value = header[colon + 1:].strip()For one delimiter, split(":", 1) is often simpler. Use a parser for formats where delimiters may be quoted, escaped, nested, or malformed.
Searching a document section
document = "TITLEnINTRODUCTIONnBODYnCONCLUSION"
body_start = document.find("BODY")
conclusion_start = document.find("CONCLUSION")
if body_start != -1 and conclusion_start != -1:
body = document[body_start:conclusion_start]Do not use substring offsets as a substitute for an HTML, JSON, XML, CSV, URL, or other format-specific parser.
Choosing related methods
| Requirement | Tool | Reason |
|---|---|---|
| Boolean membership | in |
Communicates an existence test. |
| First index, absence is normal | find() |
Returns an index or -1. |
| Missing text is an error | index() |
Raises ValueError. |
| Rightmost index | rfind() |
Searches from the right. |
| Prefix or suffix | startswith() / endswith() |
Expresses the exact test. |
| Number of non-overlapping matches | count() |
Returns a count, not positions. |
| Pattern matching | re.search() |
Supports regular-expression syntax. |
| Filesystem path components | pathlib |
Handles path semantics safely. |
Common mistakes to avoid
- Testing
if text.find(...); index0is falsey. - Slicing with
text[text.find("missing"):];-1unexpectedly starts at the last character. - Forgetting that matching is case-sensitive.
- Using
find()for a prefix or suffix instead ofstartswith()orendswith(). - Advancing repeated searches by
+1when non-overlapping matches are required, or by+len(needle)when overlaps are required. - Allowing an empty user query unintentionally.
- Mixing
strandbytes. - Assuming substring search recognizes words, grammar, or structured data.
Quick decision guide
Use find() when you need the first literal substring position, optional bounds, and ordinary -1 handling. Use in for a Boolean answer, index() when absence should raise, rfind() for the last occurrence, dedicated prefix/suffix methods for boundary checks, regular expressions for patterns, and format-aware parsers for structured input. The current Python documentation for these behaviors is available at docs.python.org.
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