~と…た・~たら…た・~たところ (discovery)
Describe what you discovered after doing something
You’ll be able to report a result or discovery after an action, and distinguish ~たところ followed by a result from ~たところだ meaning “just finished.”

カーテンを開けたら、外に雪が積もっていました。
kaaten o aketara, soto ni yuki ga tsumotte imashita.
What do you think this sentence means?
When I opened the curtains, I found snow piled up outside.
Discover an unexpected result
~と…た, ~たら…た, and ~たところ can report an unexpected result discovered after doing something. The second event is often a fact the speaker notices, not a planned consequence.
家に帰ると、母が来ていました。
ie ni kaeru to, haha ga kite imashita.
When I got home, I found that my mother had come over.
店に電話したところ、今日は休みでした。
mise ni denwa shita tokoro, kyou wa yasumi deshita.
When I called the shop, I found out it was closed today.
Put the action before the discovery
Use dictionary form + と, past plain form + ら, or past plain form + ところ followed by the discovered result. ~たところだ without a following result instead means “have just finished,” so keep the two uses separate.
駅に着いたところ、電車はもう出たあとでした。
eki ni tsuita tokoro, densha wa mou deta ato deshita.
When I arrived at the station, I found that the train had already left.
~たところ、vs ~たところだ
The same ~たところ changes meaning with what follows. With a result after it, it reports what you found; ending the sentence with だ/です, it only says the action has just finished.
~たところ、, when I did …, I found
箱を開けたところ、中は空でした。
hako o aketa tokoro, naka wa kara deshita.
When I opened the box, I found it was empty.
A result follows, so this reports a discovery.
~たところだ, have just done
箱を開けたところです。
hako o aketa tokoro desu.
I have just opened the box.
Nothing follows, so this only says the opening has just happened.
郵便受けを開けると、知らない人からの手紙が入っていました。
yuubin’uke o akeru to, shiranai hito kara no tegami ga haitte imashita.
When I opened the mailbox, there was a letter from someone I didn’t know.
医者に診てもらったところ、骨は折れていませんでした。
isha ni mite moratta tokoro, hone wa orete imasen deshita.
When I had a doctor examine me, it turned out my bone wasn’t broken.
冷蔵庫を開けたら、牛乳がなくなっていた。
reizouko o aketara, gyuunyuu ga naku natte ita.
When I opened the fridge, I found the milk was gone.
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